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Article

Expression Analysis of the ABF Gene Family in Actinidia chinensis Under Drought Stress and the Response Mechanism to Abscisic Acid

by
Haoyu Wang
1,†,
Yinqiang Zi
1,†,
Xu Rong
2,†,
Qian Zhang
3,
Lili Nie
3,
Jie Wang
1,
Hailin Ren
1,
Hanyao Zhang
1,* and
Xiaozhen Liu
3,*
1
Key Laboratory for Forest Resources Conservation and Utilization in the Southwest Mountains of China, Ministry of Education, Southwest Forestry University, Kunming 650224, China
2
School of Chemical, Biological and Environmental, Yuxi Normal University, Yuxi 653100, China
3
Key Laboratory of Biodiversity Conservation in Southwest China, National Forest and Grassland Administration, Southwest Forestry University, Kunming 650224, China
*
Authors to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Horticulturae 2025, 11(7), 715; https://doi.org/10.3390/horticulturae11070715
Submission received: 7 May 2025 / Revised: 9 June 2025 / Accepted: 18 June 2025 / Published: 20 June 2025
(This article belongs to the Special Issue Biotic and Abiotic Stress Responses of Horticultural Plants)
Browse Figures
Versions Notes

Abstract

Drought can limit plant growth. The ABRE binding factor (ABF) gene family is extensively involved in multifarious bioregulatory processes in plants. However, kiwifruit has not yet been systematically analyzed. This study analyzed the response of kiwifruit AcABF genes to drought stress. Eleven AcABF genes were distributed on nine chromosomes and clustered into three subfamilies with Arabidopsis AtABF genes, AcABF2, AcABF3, AcABF8, AcABF9, and AcABF10, which have drought resistance functions, and AtABF1, AtABF2, AtABF3, and AtABF4 were clustered in Group I. The structural domains of the nine ABF genes in Group I were highly conserved, and the protein structures were highly similar. In the analysis of the five AcABF genes in Group I, all of their cis-acting elements were related to ABA, the content of ABA-like hormones was significantly increased after drought stress, and most of the GO (Gene Ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) enrichment results were related to hormonal processes. A total of six AcABF genes were upregulated under drought stress. qRT-PCR was performed to validate the AcABF genes of Group I. The correlation coefficients of the results with the transcriptome data were all above 0.70, and the expression level of ABA increased under drought treatment. These results indicated that the five AcABF genes were positively correlated with ABA under drought stress and that, by synthesizing ABA and facilitating the expression of ABF gene family members, the tolerance of kiwifruit increased. These results provide a solid foundation for further research on improving drought tolerance in kiwifruit.

1. Introduction

Actinidia chinensis is an edible berry that originated in China [1]. Various vitamins, minerals, amino acids, and other metabolites are believed to be beneficial to human health [2]. More than 90% of the world’s kiwifruit is exported from New Zealand and Chile, with Italy exporting approximately 75% [3]. Kiwifruit has become one of the most popular fruits worldwide. ‘Hongyang’ kiwifruit, also known as red kiwifruit/red heart kiwifruit, is characterized by a medium to the skin color is darker color; short cylindrical fruits with greenish-brown, hairless skin; a very high sugar–acid ratio; and abundant anthocyanins. It has been widely cultivated for its high economic value [4,5].
Drought is a widespread environmental stress in the environment that severely hampers the growth and development of crops. Under drought stress, plant foliage will fall, curl, and wither, and stems will also bend, resulting in slow plant growth [6,7] and even a decrease in yield and quality, especially for major food crops such as wheat and corn, which are the main limiting factors for global food security and crop productivity [8,9]. Kiwifruit is relatively sensitive to arid environments, and many kiwifruit planting areas, including China, often experience drought stress [10]. Drought stress is one of the most important abiotic stresses affecting kiwifruit growth, development, and yield [11]. Plant drought stress includes moderate drought (40–45% of field water holding capacity) and severe drought (25–30% of field water holding capacity) [12]. The most obvious impact of drought stress on plants is through accelerating the transpiration rate, reducing photosynthesis, severely damaging the photosynthetic apparatus, reducing seed germination, and decreasing nutrient absorption [13,14]. To cope with survival and adversity pressures, plants must utilize a series of physiological and biochemical processes to adapt to environmental stresses. These processes are mediated through the activation or inhibition of gene-specific expression [15].
ABA (abscisic acid) is a plant hormone that accumulates under drought-induced osmotic stress conditions and plays a vital role in stress response and tolerance [16,17]. During plant growth, endogenous ABA content increase with unfavorable environmental conditions; for instance, salt stress bring about an increase in ABA concentration, prompting the activation of the ABA signaling pathway to alter downstream response of gene expression in salt-stressed environments [18,19]. It also promotes seed dormancy, inhibits seed germination, promotes stomatal closure, regulates root development, promotes tissue abscission, and defends against abiotic stressors such as drought, osmotic, and salt stress [20]. ABA signaling modulates the accumulation of other adaptive responses, such as osmoprotectants and antioxidants, in plants, further increasing their tolerance to drought [21].
The bZIP (basic region/leucine zipper motif) gene family has a large variety, percentage, and number of members [22]. Plant bZIP transcription factors are involved in the regulation of processes including but not limited to defense against pathogens, light and stress signaling, and seed and flower growth and development [23]. TFs (transcription factors) constitute one of the gene-specific expression pathways that not only interact with cis-acting elements but also activate or repress the specific expression of genes related to environmental stresses to maintain normal plant life activities [24]. The ABF gene family is a subfamily of ABA response element-binding factors and bZIP transcription factors in plants. The ABF gene family plays crucial roles in ABA-dependent and ABA-independent signaling pathways and has a variety of downstream target genes that participate in the growth and development of plants and the response to adversity and stress [25,26]. ABF upregulates ABA-regulated genes through binding to ABRE cis-acting elements [27,28]. The ABF gene family has been identified in some species through previous studies, and all of these genes can act as crucial ABA signaling pathway transcription factors in response to abiotic stressors, such as salt, drought, and low temperature [29]. For example, BnaABF2 identified in Arabidopsis enhances its tolerance to salt and drought via the modulation of ABA-dependent stress signaling genes [30]. Most of the TaABF genes identified in wheat are highly expressed and upregulated in various tissues under abiotic stress conditions, such as low nitrogen, low temperature, and drought [31]. Many cis-acting elements have been postulated in the ABF genes identified in three orchids, and ABA (ABRE) and ET (ERE) motifs were the most enriched among all the ABF genes [32]. All ten SlABF gene family members identified in tomatoes are responsive to ABA, and SlABF3 demonstrated peak sensitivity to salt stress and low-temperature stress, with concurrent activation observed in SlABF5 and SlABF10 [25]. Eight CoABF genes have been detected and characterized in jute; CoABFs are widely involved in hormone response elements, and the expression levels of CoABF3 and CoABF7 show a positive correlation with ABA concentration under ABA treatment [28]. However, few studies have investigated the changes in the expression profile of the ABF gene family and ABA concentration occurring in kiwifruit under abiotic stress.
This study aimed to comprehensively investigate the members of the ABF gene family of A. chinensis by identifying them; analyzing their physicochemical properties; performing phylogenetic analysis; determining their gene structures and conserved motifs; performing cis-acting element analysis, chromosomal localization, and GO (Gene Ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) enrichment; and analyzing their expression profiles and ABA contents under drought stress. This study lays the groundwork for further understanding ABF gene evolution and function in A. chinensis.

2. Materials and Methods

2.1. Plant Material

In this study, A. chinensis cv. ‘Hongyang’ histocultured seedlings in the histocultivation room of Southwest Forestry University were used as research materials. The best-growing tissue culture-generated seedlings were selected for refinement and transplanted into flower pots for cultivation. Finally, kiwifruit seedlings whose growth was similar to that of the subsequent experimental materials were selected [33,34].

2.2. Data Acquisition

The kiwifruit (Hongyang v3) genomic data were downloaded from the Kiwifruit Genome Database (KGB; https://kiwifruitgenome.org/, accessed on 1 May 2024) [35]. The conserved structural domain (PF00170) of the ABF transcription factor family was retrieved from the Pfam database (https://www.ebi.ac.uk/interpro/entry/pfam/?search=PF00170#table, accessed on 1 May 2024) [36]. The protein sequences and genomic data of nine A. thaliana ABF gene families were obtained from the A. thaliana genome website TAIR (https://www.Arabidopsis.org/, accessed on 1 May 2024) [28]. The genomic data of rice and apple were downloaded from the genome database of rice, JGI (https://riceome.hzau.edu.cn/, accessed on 1 May 2024), and the genome databases of Rosaceae, GDR (https://www.rosaceae.org/, accessed on 1 May 2024), respectively.

2.3. Identification and Physicochemical Properties of the ABF in A. chinensis

Initially, HMMER v3.4 software’s hmmsearch tool was employed to identify sequences within the A. chinensis genome that harbor conserved structural domains characteristic of the ABF gene family (ID: to minimize the risk of false positives, we employed protein sequences with an E value below 1 × 10−20 as a filtering criterion, as detailed in reference [37]). Next, the BLASTP module within the TBtools v2.154 suite was employed to perform a sequence comparison of A. chinensis genome-derived protein sequences by aligning them against the reference set of A. thaliana ABF gene family proteins. A comprehensive analysis was conducted to compare the protein sequences of A. chinensis, which exhibited high similarity (E value < 1 × 10−5) to those of the A. thaliana ABF gene family [38]. The hmmsearch program of the HMMER software was applied to search the protein sequences of the conserved structural domains (ID: PF00170) of the A. chinensis genomic protein data. A search for conserved structural domains within the A. chinensis protein sequences was conducted using the HMMER-based hmmsearch tool, which was applied to BLAST-identified data. The proteins whose sequences exhibited an E-value threshold of less than 1 × 10−5 were selected for further analysis. In the final stage, the protein sequences derived from the two preceding processes were integrated to generate a comprehensive profile of the ABF gene family in A. chinensis. The structural domain of ABF was validated through the CDD tool available on NCBI’s database (https://www.ncbi.nlm.nih.gov/Structure/cdd/wrpsb.cgi, accessed on 1 May 2024) as part of the NCBI sequence analysis. To isolate the ABF gene family members from A. chinensis, researchers utilized a method that involved eliminating non-existent or incomplete structural domains within the ABF gene. These genes were assigned the designation AcABF1-AcABF11 based on their chromosomal locations and were subsequently subjected to molecular weight analysis. To analyze the properties of the protein, we will evaluate the number of amino acids present in the sequence, determine the isoelectric point, calculate the stability coefficient, and assess hydrophobicity using the online tool ProtParam (https://web.expasy.org/protparam/, accessed on 1 May 2024).

2.4. Multiple Sequence Alignment, Phylogenetic Analysis, and Three-Dimensional Structure Analysis of Proteins

Initially, 11 A. chinensis AcABF gene sequences, which were identified through prior research, were selected for pairwise sequence analysis and subsequent trimming using TBtools v2.154. This process was conducted in conjunction with MEGA11.0 software to refine the dataset [38]. Subsequently, phylogenetic trees were developed using the maximum likelihood (ML) approach with MEGA11.0 software and the IQtree algorithm. In conclusion, the evolutionary tree was constructed using the Chiplot tool (https://www.chiplot.online/, accessed on 1 May 2024), which allows for the visualization and analysis of phylogenetic relationships, and subsequently, the 11 A. chinensis ABF genes were classified in accordance with the known gene clustering patterns observed in the A. thaliana species.

2.5. Gene Structure and Conserved Motif Analysis

To further analyze the gene structure and composition of the conserved motifs in the A. chinensis ABF gene family, the gene structure of each gene was analyzed according to the kiwifruit genome annotation file (GFF3) using TBtools v2.154 software [35]. The conserved motifs contained in the A. chinensis ABF genes were also predicted via the online motif prediction tool MEME (https://meme-suite.org/meme/, accessed on 1 May 2024). Visualization was then performed using TBtools software.

2.6. Analysis of Promoter Cis-Acting Elements

Nucleotide sequences 2000 bp upstream of each A. chinensis ABF gene were extracted from the A. chinensis genome annotation file (GFF3) file using TBtools software and analyzed for promoter cis-acting elements via the online software PlantCARE (https://bioinformatics.psb.ugent.be/webtools/plantcare/html/, (accessed on 1 May 2024) for promoter cis-acting element analysis.

2.7. Chromosome Localization and Covariate Partitioning

The chromosomal positions of AcABF genes were mapped using TBtools based on the A. chinensis genome annotation (GFF3 file). Subsequently, TBtools was used to extract their genomic features (length, position, and density) and to analyze collinear relationships among ABF family members (using the MCSanX plugin v4.1.0). For interspecies collinearity analysis, GFF files and gene sequences of A. thaliana, rice (Oryza sativa), and apple (Malus domestica) were downloaded from TAIR, JGI, and GDR, respectively, and analyzed using TBtools v2.154.

2.8. Transcriptome Sequencing and ABA Content Determination

In this study, 18 kiwifruit seedlings of uniform size were selected as experimental materials. The eighteen kiwifruit seedlings were divided into two groups of nine plants each, of which nine plants were used as the control group, with the soil humidity maintained at 80–85%, and were then divided into three groups numbered CK1, CK2, and CK3; the other nine plants were subjected to drought treatment, where watering was discontinued until the soil humidity reached 40–45% [12], and were subjected to drought stress for 72 h. In addition to the drought treatment, the other nine plants were randomly divided into three groups numbered T1, T2, and T3. Indices such as the plant height and leaf relative water content were observed and recorded for each group. The leaves of each sample were removed, stored in liquid nitrogen, and then transferred to Wuhan Maiwei Metabolism Technology Co., Ltd. (Wuhan, China) for sequencing of the transcriptome and determination of the content of the phytohormone (ABA). After the transcriptome data were obtained, the expression data were standardized to ensure comparability of the expression levels, genes were clustered based on expression patterns, and heatmaps were drawn for visual adjustment. After obtaining the metabolic data, the data were standardized, and p-values were obtained using T-TST.

2.9. qRT-PCR Analysis

To further verify the expressions of the AcABF2, AcABF3, AcABF5, AcABF8, AcABF9, and AcABF10 genes under drought stress, kiwifruit leaves grown at 80–85% soil moisture were used as the control groups (CK1, CK2, and CK3), and kiwifruit leaves grown under drought stress were used as the treatment groups (T1, T2, and T3). Total RNA from kiwifruit leaves was extracted with the Plant RNA Extraction Kit (DP432) (Tiangen Biochemical Technology (Beijing) Co., Ltd., Beijing, China) and reverse-transcribed into complementary DNA (cDNA) using the FastKing RT Kit (KR116) (Tiangen Biochemical Technology (Beijing) Co., Ltd., Beijing, China). Actin was used as an internal reference gene, and qRT-PCR primers (Table S1) were designed using Primer 6.0. Standard RT-PCR was then performed using a QIAGEN kit, with at least three replicates for each gene. All the data were processed and analyzed using SPASS v21 software. The reaction system was a 10 µL total reaction volume, and the mixture included 5 µL of 2× SYBR Green PCR Master Mix, 0.05 µL of QN ROX Reference Dye (Applied Biosystems instruments only), 0.7 µL of Primer A, 0.7 µL of Primer B, 2.55 µL of RNase-free water, and 1 µL of template gDNA or cDNA. The PCR procedure was as follows: predenaturation at 95 °C for 2 min; denaturation at 95 °C for 5 s; and annealing at 60 °C for 30 s, for a total of 40 cycles. Each gene was subjected to three repeated tests. The ACTIN gene was used as an internal standard, and the quantitative data were analyzed via the 2−ΔΔCT method. The primers used for qRT-PCR are listed in Supplementary Table S1.

3. Results

3.1. Identification and Physicochemical Properties of the ABF Gene Family in A. chinensis

On the basis of their positions on the chromosome, 11 ABF genes were ultimately identified and named AcABF1–ACABF11 according to their locations. The aligned A. thaliana ABF gene protein sequences were further analyzed with A. chinensis ABF protein sequences, and the structures are shown (Figure 1, Table S2). The protein length of each A. chinensis ABF gene varied widely, ranging from 50 (AcABF7) to 717 (AcABF6) amino acids; the molecular weight varied from 10.63 (AcABF4) to 81.29 (AcABF6) kiloDalton (kDa); the isoelectric point (pI) ranged from 8.42 (AcABF1) to 10.96 (AcABF4); the instability index ranged from 37.51 (AcABF7) to 69.39 (AcABF10); and the lipolysis index ranged from 50.20 (AcABF7) to 84.81 (AcABF6). The physicochemical properties of the AtABF1, AtABF2, AtABF3, and AtABF4 genes in A. thaliana and the AcABF2, AcABF3, AcABF8, and AcABF9 genes in kiwifruit are similar. It can be hypothesized that the A. thaliana AtABF1, AtABF2, AtABF3, and AtABF4 genes have similar properties to the A. chinensis AcABF2, AcABF3, AcABF8, and AcABF9 genes.

3.2. Phylogenetic Analysis of the ABF Gene Family of A. chinensis

To understand the correlations among the ABF genes of different species, the amino acid sequences encoded by 11 A. chinensis ABF genes and 9 A. thaliana ABF genes were compared to construct a phylogenetic tree. The clustering results (Figure 2a) revealed that according to the three ABF subfamilies of A. thaliana, the A. chinensis ABF genes were also categorized into three subfamilies, and each subfamily included ABF genes from both species. According to the gene data of each subfamily, the Group I subfamily had the greatest number of genes (10), in which the number of genes of A. thaliana was the same as that of A. chinensis, both with five genes; the number of genes in the Group II and Group III subfamilies was the same (both with ten genes), and the number of genes in each subfamily was the same for both A. thaliana and kiwifruit. Kiwifruit also presented the same percentage of genes in each subfamily: three A. thaliana genes and two A. chinensis genes. Based on Figure 1, correlation analysis revealed that these genes may have similar properties; the A. thaliana AtABF1, AtABF2, AtABF3, and AtABF4 genes and the A. chinensis AcABF2, AcABF3, AcABF8, AcABF9, and AcABF10 genes clustered together in subfamily I, which increases the possibility that these genes have similar properties. The A. thaliana AtABF1, AtABF2, AtABF3, and AtABF4 genes have all been shown to function in response to drought via ABA, as revealed in previous studies [39,40,41]. These findings suggest that AcABF2, AcABF3, AcABF8, AcABF9, and AcABF10 may also have similar functions, such as drought resistance.
Proteins with similar structural sequences have conserved three-dimensional structures, and conserved structural domains in different proteins have conserved functions. The protein tertiary structures of AtABF1, AtABF2, AtABF4, AtABF3, AcABF2, AcABF3, AcABF8, AcABF9, and AcABF10 were constructed using SWISS-Model 2022 software. The results (Figure 3) revealed that the protein structures of the ABF genes of clade I were highly similar, having α-helix consistency over 70% with very close ratios of α-helices, β-folds, elongated strands, and free curls. These findings suggest that the structural domains of subclass I ABF proteins from A. thaliana and kiwifruit are similar and have conserved functions.

3.3. Analysis of the Gene Structure and Conserved Motifs of the A. chinensis ABF Gene Family

To characterize the amino acid sequence of the AcABF gene family, the gene composition of this protein sequence was analyzed via the MEME Suit 5.5.8 online tool. The results are shown in Figure 4b. Conserved motifs 1 and 8 are highly conserved. Additionally, all the AREB/ABFs from Group I are extremely similar except for AcBF10. However, the same motifs have different positions in different protein sequences, which are presumed to be related to the structure and function of this protein. Combined with the phylogenetic tree of AcABF (Figure 2a), the motif distribution of members of the same subfamily also showed some differences; for example, AcABF4, AcABF5, and AcABF7 belong to subfamily II, but motif 3 appeared only in AcABF5, which might be caused by the differences between transcription factor families under specific conditions. Similarly, in subfamily III, AcABF1 and AcABF6 differ by only one motif, 4. In subfamily III, AcABF1 and AcABF6 contain five or more motifs, but AcABF11 has only two motifs, which is hypothesized to be due to the unique evolutionary process related to this subfamily.
The distribution of conserved motifs in the AcABF gene family may also be influenced by gene structure. The key to studying evolution within gene families is the distribution of gene structure. Sequence comparison of the 11 AcABF genes and analysis based on gene structure revealed (Figure 4c) that 9 of the 11 AcABF gene family members (AcABF2, AcABF3, AcABF4, AcABF5, AcABF7, AcABF8, AcABF9, AcABF10, and AcABF11) were within 7.5 kb in length. The remaining two AcABF gene family members (AcABF1 and AcABF6) were approximately 16 kb and 24 kb long, respectively. The difference in the number of introns and exons of A. chinensis ABF genes was not large, with the number of introns ranging from 1 to 8 and the number of exons ranging from 2 to 9. Among the AcABF gene family members, AcABF6 not only had the longest gene length but also contained the greatest number of introns and exons. These results suggest that different AcABF gene family members may be functionally differentiated.

3.4. Analysis of the Promoter Cis-Acting Elements of the A. chinensis ABF Gene Family

To investigate the response mechanism of A. chinensis ABF genes, 11 promoter cis-acting elements 2000 bp upstream of A. chinensis genes were predicted via the online software PlantCARE (https://bioinformatics.psb.ugent.be/webtools/plantcare/html/, accessed on 1 May 2024). The results (Figure 5) revealed 177 cis-acting elements, which could be divided into four categories: 80 light-responsive elements, 65 phytohormone-responsive elements, 26 environmental stress-responsive elements, and 6 plant-specific regulator-responsive elements. The proportion of these elements, from largest to smallest, was as follows: light-responsive elements (45%) > phytohormone-responsive elements (36%) > environmental stress-responsive elements (15%) > plant-specific regulatory elements (7%). Among the phytohormone elements, the main ones were ABA responsive elements, JA-responsive elements, and SA-responsive elements. Among them, the class I subclade AcABF genes (AcABF2, AcABF3, AcABF8, AcABF9, and AcABF10) all had ABA response elements, and the A. thaliana AtABF1, AtABF2, AtABF3, and AtABF4 genes respond to drought stress through ABA, whereas the A. chinensis AcABF2, AcABF3, AcABF8, AcABF9, and AcABF10 genes also have ABA responsive elements; thus, these five genes may also have similar drought resistance functions. Among the 11 AcABF gene family members, the maximum number of individual cis-acting response elements was eight, and the minimum was zero. Two genes, AcABF2 and AcABF9, had the maximum number of eight light response elements, and AcABF5 also had the maximum number of eight MeJA (methyl jasmonate) response elements. In summary, in addition to light-responsive elements, 54.8% of promoter-acting elements can regulate gene expression and material metabolism in plants to increase their resistance and improve their maladaptability to adverse environments.

3.5. Chromosomal Localization and Interspecific Covariance of the ABF Gene Family in A. chinensis

The results of chromosome localization revealed (Figure 6a) that the 11 ABF genes of A. chinensis were unevenly distributed on nine chromosomes. In addition, the ABF gene covariance among A. chinensis, rice, A. thaliana, and apple was also analyzed in this study, and the results (Figure 6b) revealed that A. chinensis and A. thaliana presented the greatest number of homologous gene pairs and that A. chinensis and rice presented the smallest number of homologous gene pairs. These findings indicate that the evolutionary relationship between the A. chinensis ABF and the A. thaliana ABF is relatively close and that the evolutionary relationship between the A. chinensis ABF and the rice ABF is strong.

3.6. GO Function Enrichment Analysis

GO enrichment analysis helps to understand the various potential molecular functions of gene-encoded proteins to understand the functions of genes. The DEGs (differentially expressed genes) were analyzed via GO enrichment based on the transcriptome data to understand the regulatory role of A. chinensis genes under stress. The results (Figure 7) present A. chinensis hormone processes under drought stress, such as GO:0009738 (abscisic acid-activated signaling pathway), GO:0009725 (response to hormone), GO:0009755 (hormone-mediated signaling pathway), and GO:0032870 (cellular response to hormone stimulus), among others. These results indicated that the biological processes associated with hormones were closely related to drought stress in A. chinensis and that the expression of all of these hormones was upregulated. The AcABF genes were annotated into three categories: biological process, cellular component, and molecular function. Among the biological process terms, most were related to hormone biological processes and osmoregulation; among the cellular component terms, most were related to biofilms. These findings suggest that ABF genes may adapt plants to adverse environments mainly by regulating ABA hormone levels and regulating the osmotic potential within the cell body.

3.7. Changes in the ABA Content in Kiwifruit Leaves Under Drought Stress

Abscisic acid (ABA) regulates plant growth and development and adaptation to biotic and abiotic stresses. In this study, we determined the expression of abscisic acid phytohormones in the drought stress and control groups, and the results revealed that the expressions of ABA, ABA-GE (ABA-glucosyl ester), and ABA-ald (abscisic aldehyde) in kiwifruit were significantly greater than in the control group after drought stress (Figure 8, Table S3).

3.8. KEGG Enrichment of the ABF Gene Family in A. chinensis Under Drought Stress

KEGG enrichment analysis was performed under drought stress to understand the biological function of AcABF genes under drought stress. KEGG enrichment analysis (Figure 9) revealed that the AcABF2, AcBF3, AcABF8, AcABF9, and AcABF10 genes encode ABF genes in the ABA signaling pathway. ABA response elements were found in 2000 bp in all five AcABF genes. Under drought stress, carotenoid biosynthesis occurs through multiple conversions to form abscisic acid (ABA), which is transported to the ABA receptor PYR/PYL, which directly inhibits PP2C-type protein phosphatases in the presence of ABA, thereby inhibiting SnPK2 protease activity. The inhibition of SnPK2 protease activity promotes the expression of ABF-binding factors, which facilitate the closure of leaf stomata, thereby increasing plant tolerance to drought stress. These findings confirm that the A. chinensis AcABF2, AcABF3, AcABF8, AcABF9, and AcABF10 genes activate relevant drought tolerance functions in response to ABA.

3.9. Expression Pattern and qRT-PCR Analysis of ABF Family Members in A. chinensis Under Drought Stress

Transcriptome sequencing was performed on kiwifruit leaves to understand the expression patterns of AcABF genes under drought stress; kiwifruit seedlings grown at 80–85% soil moisture were used as controls, and kiwifruit seedlings grown at 40–45% soil moisture for 72 h composed the experimental group. The results (Figure 10a, Table S4) revealed that eight AcABF genes were expressed under drought stress compared with the control (CK), and six genes (AcABF2, AcABF3, AcABF7, AcABF8, AcABF9, and AcABF10) were upregulated, suggesting that the AcABF genes may be positively regulated through positively regulating the effects of drought stress on kiwifruit, thus maintaining its life activities.
To further confirm the accuracy of the transcriptome data, five AcABF genes whose transcriptome data were significantly different and designated in the ABA pathway were selected for qRT-PCR verification. The results (Figure 10b, Table S5) revealed that the expressions of AcABF2, AcABF3, AcABF8, AcABF9, and AcABF10 were upregulated and that the differences were highly significant after drought stress compared with those of the control (CK). When we analyzed the correlation between the fragments per kilobase per million (FPKM) values and the qRT-PCR results from the transcriptome data (Table S6), the correlation coefficients were greater than 0.7, which indicated a strong correlation between the qRT-PCR results and the transcriptome data. These results confirmed the accuracy of the transcriptome data and verified the reliability of the differential genes in the transcriptome data. Moreover, these AcABF genes are crucial genes involved in the response of kiwifruit to drought stress.

4. Discussion

Kiwifruit is an important economic crop. Nonbiological stress can significantly reduce product quality and cause economic losses. Therefore, exploring the survival strategies and underlying coping mechanisms of kiwifruit is particularly important. Studies have shown that the AREB/ABF subfamily of the bZIP gene family can play an important role in plants under abiotic stress [29,42,43]. However, information about their properties and functions in kiwifruit, especially how they respond to drought stress, remains unclear.
In this study, we identified the ABF gene family in A. chinensis. The similarity of the A. chinensis gene family members AcABF2, AcABF3, AcABF8, AcABF9, and AcABF10 with the A. thaliana genes AtABF1, AtABF2, AtABF3, and AtABF4 with drought resistance functions was predicted via comparative analysis, and it was hypothesized that the A. chinensis AcABF2, AcABF3, AcABF8, AcABF9 and AcABF10 genes may have drought resistance functions. We also analyzed the expression patterns of the ABF gene, i.e., the AcABF gene, in A. chinensis under drought stress and the hormone (ABA) content of A. chinensis seedlings under drought stress, which can be used as a reference for the subsequent screening of drought resistance genes in kiwifruit and other related studies.
In this study, 11 ABF genes were identified in A. chinensis. However, nine ABF genes were identified in A. thaliana [44], ten in tomato [27], eight in jute [28], and nine in sweet potato [39], indicating that the number of ABF genes is independent of the genome size of different species. The Chinese kiwifruit AcABF gene family was categorized into three subfamilies based on the phylogenetic tree, and Arabidopsis AtABF1, AtABF2, AtABF3, and AtABF4 belong to the same subfamily as Chinese kiwifruit AcABF2, AcABF3, AcABF8, AcABF9, and AcABF10, assuming that AtABF1, AtABF2, AtABF3, and AtABF3 have functions similar to those of AcABF2. AtABF1, AtABF2, AtABF3, and AtABF4 [39,40,41] in the annual herb A. thaliana and GmABF3 in soybean [45]; OsABF2 and OsABF3 in the aquatic graminaceous plant rice increased the drought tolerance of the plants [46]; and the upregulation of TaABF2 and TaABF3 was induced by drought stress in cereal crop wheat, suggesting that the majority of species [44]. These findings indicate that the ABF2 and ABF3 genes of most species have the same function in response to drought stress. Notably, soybean GmABF8 not only responds to drought stress but also increases its expression under osmotic stress together with GmABF9 [47]; the relative expression levels of tomato SlABF8, SlABF9, and SlABF10 are upregulated under osmotic stress as well as salt stress, presumably because of the slight differences in the function of the ABF genes in different species [25]. The upregulation of SlABF8, SlABF9, and SlABF10 in tomatoes under salt stress was presumably due to slight differences in the functions of ABF genes in different species. The conserved motifs of AcABF3 in kiwifruit were consistent with those of AcABF9, and there were only small differences between AcABF2 and 8, so perhaps AcABF8 and AcABF9 not only have similar functions but also have some special functions. In contrast, AcABF10 has a large gap with the other genes of the family I; however, AcABF10 may still have specialized functions. Lu et al. reported that tea tree CsABF2, CsABF8, and CsABF11 are key transcription factors for drought tolerance, whereas the conserved structural domains of CsABF9 and CsABF10 are significantly different from the conserved structural domains of the other transcription factors but still strongly expressed under drought stress conditions [48]. It may even function only as a drought suppressant in kiwifruit.
Gene structure analysis revealed that the difference in the number of introns in each of the A. chinensis AcABF genes was small, with the number of introns in each of the 11 AcABF genes ranging from 1 to 8. This gene is similar to the ABF gene in orchids [32], poplars [49], and carrots [50]. The gene structures of the ABF genes in clade I are highly similar to the conserved motifs, which further suggests that the more similar the genes are in evolution, the more similar they are in function, thus helping to screen for functionally similar ABF genes. For example, the 13 TaABF genes in wheat are regulated by 11 known miRNAs and play important roles in abiotic stress resistance, such as drought and salt stress [31]; the overexpression of PtrABF in tobacco enhances tolerance to dehydration shock and prolonged water stress (drought) [51]; the family of CsABF genes in tea trees regulates downstream genes by modulating them and generating a resistance response, such as the drought expression levels of CsABF2, CsABF8, CsABF9, and CsABF13, which are significantly upregulated under treatment; CsABF6 and CsABF7 are notably upregulated under cold stress treatment for part of the period; and CsABF1, CsABF6, and CsABF9 are elevated under salt stress treatment, with CsABF6 reaching the highest expression at the 48 h level [48]. It can be hypothesized that AcABF genes play important roles in regulating abiotic stresses, including drought stress.
Promoter cis-acting elements are crucial for transcription and gene expression regulation in plants. In this study, a variety of resistance-related cis-acting elements were identified in the 2000 bp sequence upstream of the A. chinensis ABF gene. Among them, the phytohormone response elements were the most abundant, mainly methyl jasmonate (MeJA), ABA, salicylic acid (SA), growth hormone and gibberellin-related response elements, which suggests that the expression of AcABF genes under drought stress may be related to these hormones; among them, all genes in group I have ABA response elements, indicating that the AcABF genes of group I may be involved in the ABA transduction process. This finding is consistent with the findings concerning AREB/ABF genes and ABA [28,43,52]. Studies have shown that the bZIP (ABF) family is vital for the regulation of secondary metabolism, such as jasmonic acid (JA), carotenoids, and abscisic acid (ABA) [53,54,55,56,57]. Both MeJA and ABA can stimulate the expression of plant defense genes, inducing chemical defenses and some physiological and functional stress responses in plants [58,59,60,61]. Arabidopsis AtABF can be induced by light, ABA, and stress [43,62,63]. Potato StABF1 can be induced by ABA, drought, cold, and salt stresses to act as a homeopathic element [64], and the expression of orchid ABF genes correlates with ABA, JA, and ET [32]. ABA, MEJA, and SA have been shown, by previous researchers, to initiate their own defense responses during mechanical damage and pathogen invasion, and eventually, plants achieve rebalancing of the intracellular environment under stress conditions through the expression of stress-related genes, secondary metabolic shifts, and the accumulation of antioxidants to achieve the ability to survive and, thus, improve the resistance of the plant [65,66]. The above analyses mutually confirmed that ABF genes contribute to drought tolerance in kiwifruit. GO enrichment analysis helped elucidate the biological processes in which the AcABF gene family is involved, and the results revealed that these genes are involved mainly in biological processes, which are closely related mainly to hormones and plant resistance, and the results of the analyses further corroborated the above results.
Studying the expression patterns of relevant genes based on transcriptomic data is a new approach. In this study, we analyzed the expression patterns of kiwifruit ABF genes under drought stress. All 11 AcABF genes presented differential changes in expression under drought stress, and 6 genes were significantly upregulated (Figure 10a). Among the significantly upregulated genes, five, which were clustered in the same subfamily as the A. thaliana ABF genes with clear drought resistance functions, were selected for qRT-PCR validation in conjunction with the above conjecture validation. The correlation between the results of qRT-PCR and the results of transcriptome sequencing was high, confirming the accuracy of the transcriptome data and verifying the reliability of the transcriptome data with the DEGs (Figure 10b). These DEGs were able to respond to kiwifruit drought stress.
ABA is key in the abiotic stress response [36]. ABA accumulates to varying degrees and can mediate abiotic stress through selective splicing when plants are subjected to environmental stressors such as drought, salinity, and extreme temperatures [36,67,68]. Therefore, when plants are subjected to drought stress for a long period of time, they can be maintained by increasing the level of ABA and inducing defoliation, for example. The presence of some genes under short-term environmental stress can contribute to the maintenance of carotenoid homeostasis and accumulation, protect plants from environmental stress, and improve their tolerance to environmental stress by controlling carotenoid biosynthesis [69]. In this study, the ABA content in kiwifruit leaves under drought stress was determined (Figure 8). The results revealed that the ABA content in kiwifruit leaves significantly increased under drought stress.
ABA synthesis occurs through the carotenoid pathway [70]. It is also one of the most crucial hormones in the plant’s response to stress, and it plays a vital role in various physiological processes of the plant’s life cycle and response to biotic and abiotic stresses [70,71,72]. These findings suggest that under abiotic stress, plants synthesize ABA in various organs and initiate defense mechanisms to regulate the stomatal aperture and the expression of defense-related genes, thereby conferring resistance to environmental stress [73]. Plants synthesize ABA through the carotenoid pathway, and when plants are subjected to drought stress, dehydrated roots increase their water absorption capacity by synthesizing ABA, thereby inhibiting lateral root growth and promoting deep root production [74]. ABA enhances plant drought tolerance by regulating stomata; reducing water loss, such as transpiration; increasing plant water use efficiency; and activating ABA-dependent gene regulatory networks [75]. ABA response element-binding factor (ABRE binding factor (ABF)) is a downstream target gene for ABA-dependent pathways [76]. The expression of the ABF binding factor promotes leaf stoma closure, increasing plant tolerance to drought stress.
Abscisic acid (ABA) regulates many crucial processes in plant development and adaptation to biotic and abiotic stresses. Under stress conditions, plants synthesize ABA in various organs and initiate defense mechanisms, such as the regulation of the stomatal aperture and the expression of defense-related genes [73]. The drought-induced increase in ABA in plant cells is synthesized mainly by defense cells through the carotenoid pathway, and the accumulated ABA is sensed by the receptor pyrabactin (PYR/PYL). The binding affinity of ABA-PYR/PYL is regulated by phosphatases (PP2Cs), which are considered ABA coreceptors, and PP2Cs play a negative role in ABA signaling through the inhibition of downstream targets [77]. ABA signaling plays a negative role in ABA signaling [78]. ABA-bound receptors form a complex with the plant protein phosphatase 2C phosphatase of type 2C (PP2C), which deregulates the inhibitory effect of PP2C on the related protein kinase 2 (SnRK2) protein kinase [78]. SnRK2 is then phosphorylated via autophosphorylation or other protein kinases (e.g., Raf-like MAPKKK). The phosphorylated state of SnRK2 activates the transcription factor ABA responsive element-binding factors (AREB/ABFs) through phosphorylation, thereby regulating various transcriptional and posttranslational levels of physiological responses, such as seed maturation, leaf genesis, stem cell maintenance, stomatal movement, photosynthesis, carbon translocation, bud dormancy, flowering, fruit maturation, and senescence [79]. Kang et al. [80] and others have shown that overexpression of the AtABF3 and AtABF4 genes enhances tolerance to drought stress in Arabidopsis. Based on the phylogenetic tree, KEGG enrichment analysis, transcriptional data, and expression of ABA in the leaves of rhesus macaques after drought stress in this study, as well as [78] the coevolution of hormone metabolism and signaling networks, expanded plant adaptive plasticity, we can speculate a mechanistic model diagram of AcABF (AcABF2, AcABF3, AcABF8, AcABF9, and AcABF10) genes involved in ABA signaling to increase drought tolerance in kiwifruit (Figure 11). Under drought stress, kiwifruit may synthesize large amounts of ABA through the carotenoid pathway, and ABA binds to receptors (PYR/PYL); inhibits the activities of PP2C-type protein phosphatase and SnPK2 protease; promotes the expression of ABF, an ABA transcription factor; and then promotes the closure of stomata in kiwifruit leaves to increase drought stress tolerance. The above is only speculation, and further transgenic experiments and measurements of ABA content and stomatal closure in transgenic plants are needed to prove this speculation.

5. Conclusions

In this study, 11 AcABF genes were identified from the A. chinensis genome and phylogenetically categorized into three subfamilies, and members of these gene families were unevenly distributed on nine chromosomes. GO enrichment and cis-acting element analysis revealed that the AcABF genes were associated with ABA synthesis and metabolic pathways. Nine AcABF genes were expressed under drought stress, and six AcABF genes were DEGs. The qRT-PCR results strongly correlated with the transcriptome data, with correlation coefficients greater than 0.7. The contents of ABA phytohormones such as ABA, ABA-ald, ABA-GE, and ACC significantly increased, indicating that A. chinensis synthesizes a large amount of ABA to increase its tolerance to drought. Based on KEGG enrichment, AcABF2, AcABF3, AcABF8, AcABF9, and AcABF10 were enriched in the ABA signaling pathway and identified as binding factors of ABA response elements. The mechanism by which the kiwifruit ABF gene family responds to drought stress involves increasing the content of ABA in plants by promoting the expression of the ABA transcription factor ABF to increase the tolerance of these plants to drought stress.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/horticulturae11070715/s1, Table S1. Primer design for qRT-PCR. Table S2. Physicochemical properties of AcABF genes. Table S3. Expression of kiwifruit ABA analogs under drought and control conditions. Table S4. FPKM values of AcABF genes. Table S5. Raw CT values for the qRT-PCR data. Table S6. Correlations of the transcriptome data with the qRT-PCR results.

Author Contributions

Conceptualization, investigation, formal analysis, writing—original draft preparation, and software, H.W.; conceptualization, writing—original draft preparation, and software, Y.Z.; conceptualization and writing—original draft preparation, X.R.; software and data curation, Q.Z.; material provision and sampling, L.N.; validation, J.W.; validation, H.R.; review and editing, supervision, and funding acquisition, H.Z.; methodology, writing—review and editing, and funding acquisition, X.L. All authors have read and agreed to the published version of the manuscript.

Funding

This study is supported by the Agricultural Joint Key Projects in Yunnan Province (202301BD070001-003), the Rural Revitalization Science and Technology Project-Rural Revitalization Industry Key Technology Integration Demonstration Project (202304BP090005), the Yunnan Academician (Expert) Workstation Project (202305AF150020), the Yunnan First-class Construction Discipline of Forestry Science of Southwest Forestry University, and the Start-up Fund Project of Doctoral Research at Southwest Forestry University. The funders had no role in the design of the study; the collection, analysis, or interpretation of the data; or the writing of the manuscript.

Data Availability Statement

All data generated or analyzed during this study are included in this published article. Kiwifruit genome annotation files can be accessed at http://kiwifruitgenome.org/ (accessed on 1 May 2024). RNA-Seq (RNA sequencing) data under salt stress can be found at https://submit.ncbi.nlm.nih.gov/subs/sra/SUB14697397 (accessed on 1 May 2024). The RNA-Seq data are publicly available at the National Center for Biotechnology Information. The other data presented in this study are available in the Supplementary Materials.

Acknowledgments

The authors thank Deqiang Zhang, Beijing Forestry University, for his critical reading of the manuscript.

Conflicts of Interest

The authors declare that there are no conflicts of interest regarding any commercial or financial relationships pertaining to in this study.

References

  1. Huang, S.; Ding, J.; Deng, D.; Tang, W.; Sun, H.; Liu, D.; Zhang, L.; Niu, X.; Zhang, X.; Meng, M.; et al. Draft genome of the kiwifruit Actinidia chinensis. Nat. Commun. 2013, 4, 2640. [Google Scholar] [CrossRef] [PubMed] [PubMed Central]
  2. Latocha, P.; Debersaques, F.; Decorte, J. Varietal differences in the mineral composition of kiwiberry Actinidia arguta (Siebold et Zucc.) Planch, ex. Miq. Acta Hortic. 2015, 1096, 479–486. [Google Scholar] [CrossRef]
  3. Ashraf, I.; Cipriani, G.; De Mori, G. Bridging the gap: Genetic insights into graft compatibility for enhanced kiwifruit production. Int. J. Mol. Sci. 2025, 26, 2925. [Google Scholar] [CrossRef] [PubMed]
  4. Liu, Y.; Lv, G.; Yang, Y.; Ma, K.; Ren, X.; Li, M.; Liu, Z. Interaction of AcMADS68 with transcription factors regulates anthocyanin biosynthesis in red-fleshed kiwifruit. Hortic. Res. 2022, 10, uhac252. [Google Scholar] [CrossRef] [PubMed] [PubMed Central]
  5. Bassi, I.; Mian, G.; Troiano, S.; Gori, E.; Iseppi, L. Assessing consumer preferences for new red-pulp kiwifruit: Application of a choice experiment between different countries. Foods 2023, 12, 2865. [Google Scholar] [CrossRef] [PubMed] [PubMed Central]
  6. Zhang, Y.; Zhang, H.Z.; Fu, J.Y.; Du, Y.Y.; Qu, J.; Song, Y.; Wang, P.W. The GmXTH1 gene improves drought stress resistance of soybean seedlings. Mol. Breed. 2021, 42, 3. [Google Scholar] [CrossRef]
  7. Razi, K.; Muneer, S. Drought stress-induced physiological mechanisms, signaling pathways and molecular response of chloroplasts in common vegetable crops. Crit. Rev. Biotechnol. 2021, 41, 669–691. [Google Scholar] [CrossRef]
  8. Daryanto, S.; Wang, L.; Jacinthe, P. Global synthesis of drought effects on maize and wheat production. PLoS ONE 2017, 11, e0156362. [Google Scholar] [CrossRef]
  9. Sallam, A.; Alqudah, M.A.; Dawood, A.F.M.; Baenziger, P.S.; Börner, A. Drought stress tolerance in wheat and barley: Advances in physiology, breeding and genetics Research. Int. J. Mol. Sci. 2019, 20, 3137. [Google Scholar] [CrossRef]
  10. Judd, M.J.; McAneney, K.J.; Wilson, K.S. Influence of water stress on kiwifruit growth. Irrig. Sci. 1989, 10, 303–311. [Google Scholar] [CrossRef]
  11. Chen, J.Y.; Fang, J.B.; Qi, X.J.; Gu, H.; Lin, M.M.; Zhang, W.Y.; Wei, C.G. Research progress on rootstocks of kiwifruit. J. Fruit Sci. 2015, 32, 959–968. [Google Scholar]
  12. Bao, W.W.; Chen, X.; Li, R.N.; Li, M.; Xie, C.J.; Dou, M.R.; Zhang, K.Z.; Wang, J.; Gao, Z.X.; Liu, Z.D.; et al. Comprehensive assessment of drought resistance and recovery in kiwifruit genotypes using multivariate analysis. Plant J. 2024, 119, 100–114. [Google Scholar] [CrossRef] [PubMed]
  13. Dubey, A.; Kumar, A.; Malla, M.A.; Chowdhary, K.; Singh, G.; Ravikanth, G.; Harish; Sharma, S.; Saati-Santamaria, Z.; Menéndez, E.; et al. Approaches for the amelioration of adverse effects of drought stress on crop plants. Front. Biosci. 2021, 26, 928–947. [Google Scholar] [CrossRef] [PubMed]
  14. Mukarram, M.; Choudhary, S.; Kurjak, D.; Petek, A.; Khan, M.M.A. Drought: Sensing, signalling, effects and tolerance in higher plants. Physiol. Plant. 2021, 172, 1291–1300. [Google Scholar] [CrossRef] [PubMed]
  15. Sun, X.; Wang, Y.; Sui, N. Transcriptional regulation of bHLH during plant response to stress. Biochem. Biophys. Res. Commun. 2018, 503, 397–401. [Google Scholar] [CrossRef] [PubMed]
  16. Nakashima, K.; Yamaguchi-Shinozaki, K.; Shinozaki, K. The transcriptional regulatory network in the drought response and its crosstalk in abiotic stress responses including drought, cold, and heat. Front. Plant Sci. 2014, 5, 170. [Google Scholar] [CrossRef] [PubMed] [PubMed Central]
  17. Nakashima, K.; Yamaguchi-Shinozaki, K. ABA signaling in stress-response and seed development. Plant Cell Rep. 2013, 32, 959–970. [Google Scholar] [CrossRef] [PubMed]
  18. Du, F.; Wang, Y.; Wang, J.; Li, Y.; Zhang, Y.; Zhao, X.; Xu, J.; Li, Z.; Zhao, T.; Wang, W.; et al. The basic helix-loop-helix transcription factor gene, OsbHLH38, plays a key role in controlling rice salt tolerance. J. Integr. Plant Biol. 2023, 65, 1859–1873. [Google Scholar] [CrossRef] [PubMed]
  19. Geilfus, C.M.; Mithöfer, A.; Ludwig-Müller, J.; Zörb, C.; Muehling, K.H. Chloride-inducible transient apoplastic alkalinizations induce stomatal closure by controlling abscisic acid distribution between leaf apoplast and guard cells in salt-stressed Vicia faba. New Phytol. 2015, 208, 803–816. [Google Scholar] [CrossRef] [PubMed]
  20. Brookbank, B.P.; Patel, J.; Gazzarrini, S.; Nambara, E. Role of basal aba in plant growth and Development. Genes 2021, 12, 1936. [Google Scholar] [CrossRef] [PubMed] [PubMed Central]
  21. Sato, H.; Mizoi, J.; Shinozaki, K.; Yamaguchi-Shinozaki, K. Complex plant responses to drought and heat stress under climate change. Plant. J. 2024, 117, 1873–1892. [Google Scholar] [CrossRef] [PubMed]
  22. Zhao, J.; Guo, R.; Guo, C.; Hou, H.; Wang, X.; Gao, H. Evolutionary and expression analyses of the apple basic leucine zipper transcription factor Family. Front. Plant Sci. 2016, 7, 376. [Google Scholar] [CrossRef]
  23. Jakoby, M.; Weisshaar, B.; Dröge-Laser, W.; Vicente-Carbajosa, J.; Tiedemann, J.; Kroj, T.; Parcy, F.; bZIP Research Group. bZIP transcription factors in Arabidopsis. Trends Plant Sci. 2002, 7, 106–111. [Google Scholar] [CrossRef] [PubMed]
  24. Niu, X.; Fu, D. The Roles of BLH Transcription factors in plant development and environmental Response. Int. J. Mol. Sci. 2022, 23, 3731. [Google Scholar] [CrossRef]
  25. Pan, X.; Wang, C.; Liu, Z.; Gao, R.; Feng, L.; Li, A.; Yao, K.; Liao, W. Identification of ABF/AREB gene family in tomato (Solanum lycopersicum L.) and functional analysis of ABF/AREB in response to ABA and abiotic stresses. PeerJ 2023, 11, e15310. [Google Scholar] [CrossRef] [PubMed] [PubMed Central]
  26. Chang, H.C.; Tsai, M.C.; Wu, S.S.; Chang, I.F. Regulation of ABI5 expression by ABF3 during salt stress responses in Arabidopsis thaliana. Bot. Stud. 2019, 60, 16. [Google Scholar] [CrossRef]
  27. Yoshida, T.; Fujita, Y.; Sayama, H.; Kidokoro, S.; Maruyama, K.; Mizoi, J. AREB1, AREB2, and ABF3 are master transcription factors that cooperatively regulate ABRE-dependent ABA signaling involved in drought stress tolerance and require ABA for full activation. Plant J. 2010, 61, 672–685. [Google Scholar] [CrossRef] [PubMed]
  28. Fiallos-Salguero, M.S.; Li, J.; Li, Y.; Xu, J.; Fang, P.; Wang, Y.; Zhang, L.; Tao, A. Identification of AREB/ABF gene family involved in the response of aba under salt and drought stresses in jute (Corchorus olitorius L.). Plants 2023, 12, 1161. [Google Scholar] [CrossRef] [PubMed]
  29. Fujita, Y.; Yoshida, T.; Yamaguchi-Shinozaki, K. Pivotal role of the AREB/ABF-SnRK2 pathway in ABRE-mediated transcription in response to osmotic stress in plants. Physiol. Plant. 2012, 147, 15–27. [Google Scholar] [CrossRef]
  30. Zhao, B.Y.; Hu, Y.F.; Li, J.; Yao, X.; Liu, K. BnaABF2, a bZIP transcription factor from rapeseed (Brassica napus L.), enhances drought and salt tolerance in transgenic Arabidopsis. Bot. Stud. 2016, 57, 12. [Google Scholar] [CrossRef]
  31. Yang, F.; Sun, X.; Wu, G.; He, X.; Liu, W.; Wang, Y.; Sun, Q.; Zhao, Y.; Xu, D.; Dai, X.; et al. Genome-wide identification and expression profiling of the abf transcription factor family in wheat (Triticum aestivum L.). Int. J. Mol. Sci. 2024, 25, 3783. [Google Scholar] [CrossRef] [PubMed] [PubMed Central]
  32. Xie, X.; Lin, M.; Xiao, G.; Wang, Q.; Li, Z. Identification and characterization of the AREB/ABF gene family in three orchid species and functional analysis of DcaABI5 in Arabidopsis. Plants 2024, 13, 774. [Google Scholar] [CrossRef] [PubMed] [PubMed Central]
  33. Sinkar, R.S.; Rai, M. Plant Tissue Culture:Theory and Practical Approach; CRC Press: Boca Raton, FL, USA, 2025. [Google Scholar]
  34. Loyola-Vargas, V.M.; Ochoa-Alejo, N. An Introduction to plant cell, tissue, and organ culture: Current status and perspectives. Methods Mol. Biol. 2024, 2827, 1–13. [Google Scholar] [CrossRef] [PubMed]
  35. Tao, J.; Jia, H.; Wu, M.; Zhong, W.; Jia, D.; Wang, Z. Genome-wide identification and characterization of the TIFY gene family in kiwifruit. BMC Genom. 2022, 23, 179. [Google Scholar] [CrossRef] [PubMed]
  36. Yang, Y.; Chen, L.; Su, G.; Liu, F.; Zeng, Q.; Li, R. Identification and expression analysis of the lipid phosphate phosphatases gene family reveal their involvement in abiotic stress response in kiwifruit. Front. Plant Sci. 2022, 13, 942937. [Google Scholar] [CrossRef]
  37. Potter, S.C.; Luciani, A.; Eddy, S.R.; Park, Y.; Lopez, R.; Finn, R.D. HMMER web server, 2018 update. Nucleic Acids Res. 2018, 46, W200–W204. [Google Scholar] [CrossRef]
  38. Chen, C.; Chen, H.; Zhang, Y.; Thomas, H.R.; Frank, M.H.; He, Y. TBtools, an integrative toolkit developed for interactive analyses of big biological data. Mol. Plant. 2020, 13, 1194–1202. [Google Scholar] [CrossRef]
  39. Muñiz García, M.N.; Cortelezzi, J.I.; Fumagalli, M.; Capiati, D.A. Expression of the Arabidopsis ABF4 gene in potato increases tuber yield, improves tuber quality and enhances salt and drought tolerance. Plant Mol. Biol. 2018, 98, 137–152. [Google Scholar] [CrossRef]
  40. Liu, J.; Shu, D.; Tan, Z.; Ma, M.; Guo, N.; Gao, S.; Duan, G.; Kuai, B.; Hu, Y.; Li, S.; et al. The Arabidopsis IDD14 transcription factor interacts with bZIP-type ABFs/AREBs and cooperatively regulates ABA-mediated drought tolerance. New Phytol. 2022, 236, 929–942. [Google Scholar] [CrossRef]
  41. Yoshida, T.; Fujita, Y.; Maruyama, K.; Mogami, J.; Todaka, D.; Shinozaki, K. Four Arabidopsis AREB/ABF transcription factors function predominantly in gene expression downstream of SnRK2 kinases in abscisic acid signalling in response to osmotic stress. Plant Cell Environ. 2014, 38, 35–49. [Google Scholar] [CrossRef]
  42. Maszkowska, J.; Szymańska, K.P.; Kasztelan, A.; Krzywińska, E.; Sztatelman, O.; Dobrowolska, G. The Multifaceted Regulation of SnRK2 Kinases. Cells 2021, 10, 2180. [Google Scholar] [CrossRef] [PubMed]
  43. Choi, H.; Hong, J.; Ha, J.; Kang, J.; Kim, S.Y. ABFs, a family of ABA-responsive element binding factors. J. Biol. Chem. 2000, 275, 1723–1730. [Google Scholar] [CrossRef] [PubMed]
  44. Li, F.; Mei, F.; Zhang, Y.; Li, S.; Kang, Z.; Mao, H. Genome-wide analysis of the AREB/ABF gene lineage in land plants and functional analysis of TaABF3 in Arabidopsis. BMC Plant Biol. 2020, 20, 558. [Google Scholar] [CrossRef] [PubMed] [PubMed Central]
  45. Li, C.; Chen, Y.; Hu, Q.; Yang, X.; Zhao, Y.; Lin, Y.; Yuan, J.; Gu, J.; Li, Y.; He, J.; et al. Pseudoresponse regulator 3b and transcription factor ABF3 modulate abscisic acid-dependent drought stress response in soybean. Plant Physiol. 2024, 195, 3053–3071. [Google Scholar] [CrossRef]
  46. Hossain, M.A.; Cho, J.I.; Han, M.; Ahn, C.H.; Jeon, J.S.; An, G.; Park, P.B. The ABRE-binding bZIP transcription factor OsABF2 is a positive regulator of abiotic stress and ABA signaling in rice. J. Plant Physiol. 2010, 167, 1512–1520. [Google Scholar] [CrossRef] [PubMed]
  47. Zhang, B.S.; Li, M.Y.; Song, Z.; Han, J.P.; Cheng, Z.Q.; Chen, X.J.; Han, D.Z.; Hu, Z.B.; Liu, C.Y.; Yang, M.L.; et al. Characterization of the soybean ABF gene family and the key regulatory function of GmABF1 in salt stress response. Int. J. Biol. Macromol. 2025, 317, 144763. [Google Scholar] [CrossRef] [PubMed]
  48. Lu, J.; Du, J.; Tian, L.; Li, M.; Zhang, X.; Zhang, S.; Wan, X.; Chen, Q. Divergent response strategies of CsABF facing abiotic stress in tea plant: Perspectives from drought-tolerance studies. Front. Plant Sci. 2021, 12, 763843. [Google Scholar] [CrossRef] [PubMed] [PubMed Central]
  49. Ji, L.; Wang, J.; Ye, M.; Li, Y.; Guo, B.; Chen, Z.; Li, H.; An, X. Identification and characterization of the Populus AREB/ABF Subfamily. J. Integr. Plant Biol. 2013, 55, 177–186. [Google Scholar] [CrossRef] [PubMed]
  50. Wang, Y.H.; Que, F.; Li, T.; Zhang, R.R.; Khadr, A.; Xu, Z.S.; Tian, Y.S.; Xiong, A.S. DcABF3, an ABF transcription factor from carrot, alters stomatal density and reduces ABA sensitivity in transgenic Arabidopsis. Plant Sci. 2021, 302, 110699. [Google Scholar] [CrossRef] [PubMed]
  51. Huang, X.S.; Liu, J.H.; Chen, X.J. Overexpression of PtrABF gene, a bZIP transcription factor isolated from Poncirus trifoliata, enhances dehydration and drought tolerance in tobacco via scavenging ROS and modulating expression of stress-responsive genes. BMC Plant Biol. 2010, 10, 230. [Google Scholar] [CrossRef] [PubMed] [PubMed Central]
  52. Uno, Y.; Furihata, T.; Abe, H.; Yoshida, R.; Shinozaki, K.; Yamaguchi-Shinozaki, K. Arabidopsis basic leucine zipper transcription factors involved in an abscisic acid-dependent signal transduction pathway under drought and high-salinity conditions. Proc. Natl. Acad. Sci. USA 2000, 97, 11632–11637. [Google Scholar] [CrossRef] [PubMed] [PubMed Central]
  53. Cao, S.; Cai, Y.; Yang, Z.; Joyce, D.C.; Zheng, Y. Effect of MeJA treatment on polyamine, energy status and anthracnose rot of loquat fruit. Food Chem. 2014, 145, 86–89. [Google Scholar] [CrossRef] [PubMed]
  54. Berens, M.L.; Berry, H.M.; Mine, A.; Argueso, C.T.; Tsuda, K. Evolution of hormone signaling networks in plant defense. Annu. Rev. Phytopathol. 2017, 55, 401–425. [Google Scholar] [CrossRef]
  55. Laura, B.; Silvia, P.; Francesca, F.; Benedetta, S.; Carla, C. Epigenetic control of defense genes following MeJA-induced priming in rice (O. sativa). J. Plant Physiol. 2018, 228, 166–177. [Google Scholar] [CrossRef]
  56. Ma, Y.; Cao, J.; He, J.; Chen, Q.; Li, X.; Yang, Y. Molecular mechanism for the regulation of ABA homeostasis during plant development and stress Responses. Int. J. Mol. Sci. 2018, 19, 3643. [Google Scholar] [CrossRef]
  57. Osakabe, Y.; Yamaguchi-Shinozaki, K.; Shinozaki, K.; Tran, L.P. ABA control of plant macroelement membrane transport systems in response to water deficit and high salinity. New Phytol. 2014, 202, 35–49. [Google Scholar] [CrossRef]
  58. Chini, A.; Gimenez-Ibanez, S.; Goossens, A.; Solano, R. Redundancy and specificity in jasmonate signalling. Curr. Opin. Plant Biol. 2016, 33, 147–156. [Google Scholar] [CrossRef] [PubMed]
  59. Zhou, M.; Memelink, J. Jasmonate-responsive transcription factors regulating plant secondary metabolism. Biotechnol. Adv. 2016, 34, 441–449. [Google Scholar] [CrossRef]
  60. Aleman, F.; Yazaki, J.; Lee, M.; Takahashi, Y.; Kim, A.Y.; Li, Z. An ABA-increased interaction of the PYL6 ABA receptor with MYC2 transcription factor, A putative link of ABA and JA signaling. Scientific Rep. 2016, 6, 28941. [Google Scholar] [CrossRef]
  61. Walter, M.H.; Strack, D. Carotenoids and their cleavage products, biosynthesis and functions. Natural Product Rep. 2011, 28, 663–692. [Google Scholar] [CrossRef]
  62. Kim, S.; Kang, J.Y.; Cho, D.I.; Park, J.H.; Kim, S.Y. ABF2, an ABRE-binding bZIP factor, is an essential component of glucose signaling and its overexpression affects multiple stress tolerance. Plant J. 2004, 40, 75–87, Erratum in: Plant J. 2005, 43, 467. [Google Scholar] [CrossRef] [PubMed]
  63. Xu, D.; Li, J.; Gangappa, S.N.; Hettiarachchi, C.; Lin, F.; Andersson, M.X.; Jiang, Y.; Deng, X.W.; Holm, M. Convergence of Light and ABA signaling on the ABI5 promoter. PLoS Genet. 2014, 10, e1004197. [Google Scholar] [CrossRef] [PubMed] [PubMed Central]
  64. Muñiz García, M.N.; Giammaria, V.; Grandellis, C.; Téllez-Iñón, M.T.; Ulloa, R.M.; Capiati, D.A. Characterization of StABF1, a stress-responsive bZIP transcription factor from Solanum tuberosum L. that is phosphorylated by StCDPK2 vitro. Planta 2012, 235, 761–778. [Google Scholar] [CrossRef] [PubMed]
  65. Schopfer, P. Biomechanics of plant growth. Am. J. Bot. 2006, 93, 1415–1425. [Google Scholar] [CrossRef]
  66. Wang, D.; Pajerowska-Mukhtar, K.; Culler, A.H.; Dong, X. Salicylic acid inhibits pathogen growth in plants through repression of the auxin signaling Pathway. Curr. Biol. 2007, 17, 1784–1790. [Google Scholar] [CrossRef] [PubMed]
  67. Zhang, A.; Yang, X.; Lu, J.; Song, F.; Sun, J.; Wang, C.; Lian, J.; Zhao, L.; Zhao, B. OsIAA20, an Aux/IAA protein, mediates abiotic stress tolerance in rice through an ABA pathway. Plant Sci. 2021, 308, 110903. [Google Scholar] [CrossRef] [PubMed]
  68. Min, M.K.; Kim, R.; Hong, W.J.; Jung, K.H.; Le, J.Y.; Kim, B.G. OsPP2C09 is a bifunctional regulator in both ABA-dependent and independent abiotic stress signaling pathways. Int. J. Mol. Sci. 2021, 22, 393. [Google Scholar] [CrossRef] [PubMed]
  69. Kim, H.S.; Ji, C.Y.; Lee, C.J.; Kim, S.E.; Park, S.C.; Kwak, S.S. Orange: A target gene for regulating carotenoid homeostasis and increasing plant tolerance to environmental stress in marginal lands. J. Exp. Bot. 2018, 69, 3393–3400. [Google Scholar] [CrossRef] [PubMed]
  70. Guilfoyle, T.; Hagen, G.; Dong, T.; Park, Y.; Hwang, I. Abscisic acid: Biosynthesis, inactivation, homoeostasis and signalling. Essays Biochem. 2015, 58, 29–48. [Google Scholar] [CrossRef]
  71. Chernys, J.T.; Zeevaart, J.A. Characterization of the 9-cis-epoxycarotenoid dioxygenase gene family and the regulation of abscisic acid biosynthesis in avocado. Plant Physiol. 2000, 124, 343–354. [Google Scholar] [CrossRef]
  72. Zhu, J.K. Salt and drought stress signal transduction in plants. Annu. Rev. Plant Biol. 2002, 53, 247–273. [Google Scholar] [CrossRef]
  73. Lim, C.W.; Baek, W.; Jung, J.; Kim, J.H.; Lee, S.C. Function of ABA in stomatal defense against biotic and drought stresses. Int. J. Mol. Sci. 2015, 16, 15251–15270. [Google Scholar] [CrossRef] [PubMed]
  74. Lee, S.C.; Luan, S. ABA signal transduction at the crossroad of biotic and abiotic stress responses. Plant Cell Environ. 2011, 35, 53–60. [Google Scholar] [CrossRef] [PubMed]
  75. Daszkowska-golec, A.; Szarejko, I. The molecular basis of ABA-mediated plant response to drought. PLoS ONE 2013, 177, 103–134. [Google Scholar]
  76. Soma, F.; Takahashi, F.; Yamaguchi-Shinozaki, K.; Shinozaki, K. Cellular phosphorylation signaling and gene expression in drought stress responses, ABA-dependent and ABA-independent regulatory systems. Plants 2021, 10, 756. [Google Scholar] [CrossRef] [PubMed]
  77. Gong, Z.; Xiong, L.; Shi, H.; Yang, S.; Herrera-Estrella, L.R.; Xu, G. Plant abiotic stress response and nutrient use efficiency. Sci. China-Life Sci. 2020, 63, 635–674. [Google Scholar] [CrossRef] [PubMed]
  78. Weng, J.K.; Ye, M.; Li, B.; Noel, J.P. Co-evolution of hormone metabolism and signaling networks expands plant adaptive plasticity. Cell 2016, 166, 881–893. [Google Scholar] [CrossRef]
  79. Umezawa, T.; Sugiyama, N.; Takahashi, F.; Anderson, J.C.; Ishihama, Y.; Peck, S.C.; Shinozaki, K. Genetics and Phosphoproteomics Reveal a Protein Phosphorylation Network in the Abscisic Acid Signaling Pathway in Arabidopsis thaliana. Sci. Signal. 2013, 6, rs8. [Google Scholar] [CrossRef]
  80. Kang, J.Y.; Choi, H.I.; Im, M.Y.; Kim, S.Y. Arabidopsis basic leucine zipper proteins that mediate stress-responsive abscisic acid signaling. Plant Cell 2002, 14, 343–357. [Google Scholar] [CrossRef]
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Figure 1. The physicochemical property analysis of the A. thaliana ABF genes and the Actinidia chinensis ABF genes. The numbers in the heatmap indicate numerical values, with larger values being darker; the outermost circle indicates the name of the gene, followed by the aliphatic index, instability index, theoretical pI, and molecular weight (kDa).
Figure 1. The physicochemical property analysis of the A. thaliana ABF genes and the Actinidia chinensis ABF genes. The numbers in the heatmap indicate numerical values, with larger values being darker; the outermost circle indicates the name of the gene, followed by the aliphatic index, instability index, theoretical pI, and molecular weight (kDa).
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Figure 2. Phylogenetic tree of the A. thaliana and A. chinensis ABF gene families. (a) Phylogenetic tree plot constructed via the maximum likelihood (ML) method using 1000 replicated bootstrap values, with different subgroups denoted by different colors; in the figure, red denotes subfamily I, blue denotes subfamily II, green denotes subfamily III, red dots indicate AtABF genes that have been functionally validated. (b) Plot of the number of A. thaliana and A. chinensis ABF genes in each subclade, with light yellow-brown denoting subclade I, blue denoting subclade II, and red denoting subclade III.
Figure 2. Phylogenetic tree of the A. thaliana and A. chinensis ABF gene families. (a) Phylogenetic tree plot constructed via the maximum likelihood (ML) method using 1000 replicated bootstrap values, with different subgroups denoted by different colors; in the figure, red denotes subfamily I, blue denotes subfamily II, green denotes subfamily III, red dots indicate AtABF genes that have been functionally validated. (b) Plot of the number of A. thaliana and A. chinensis ABF genes in each subclade, with light yellow-brown denoting subclade I, blue denoting subclade II, and red denoting subclade III.
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Figure 3. Protein tertiary structure diagrams of AtABF1, AtABF2, AtABF3, AtABF4, AcABF2, AcABF3, AcABF8, AcABF9, and AcABF10. The upper row represents the protein tertiary structure diagrams of A. thaliana AtABF1, AtABF2, AtABF4, and AtABF3; the lower row represents the protein tertiary structure diagrams of kiwifruit AcABF2, AcABF3, AcABF8, AcABF9, and AcABF10.
Figure 3. Protein tertiary structure diagrams of AtABF1, AtABF2, AtABF3, AtABF4, AcABF2, AcABF3, AcABF8, AcABF9, and AcABF10. The upper row represents the protein tertiary structure diagrams of A. thaliana AtABF1, AtABF2, AtABF4, and AtABF3; the lower row represents the protein tertiary structure diagrams of kiwifruit AcABF2, AcABF3, AcABF8, AcABF9, and AcABF10.
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Figure 4. Conserved motifs and gene structure maps of the A. thaliana AtABF1, AtABF2, AtABF3, and AtABF4 genes and the A. chinensis ABF gene family. (a) Members of the A. thaliana AtABF1, AtABF2, AtABF3, and AtABF4 genes and the A. chinensis ABF gene family. (b) A. thaliana AtABF1, AtABF2, AtABF3, and AtABF4 genes and A. chinensis AcABF. Distribution of conserved motifs; the motifs are indicated by colored boxes, and the black lines indicate the relative lengths of the proteins. The ruler represents the length of the motif. (c) Exon-intron structure diagrams of the A. thaliana AtABF1, AtABF2, AtABF3, and AtABF4 genes and the A. chinensis AcABF genes, with green denoting the UTR, yellow showing the CDS, and the line segment in the center indicating the intron. The ruler represents the length of the genes.
Figure 4. Conserved motifs and gene structure maps of the A. thaliana AtABF1, AtABF2, AtABF3, and AtABF4 genes and the A. chinensis ABF gene family. (a) Members of the A. thaliana AtABF1, AtABF2, AtABF3, and AtABF4 genes and the A. chinensis ABF gene family. (b) A. thaliana AtABF1, AtABF2, AtABF3, and AtABF4 genes and A. chinensis AcABF. Distribution of conserved motifs; the motifs are indicated by colored boxes, and the black lines indicate the relative lengths of the proteins. The ruler represents the length of the motif. (c) Exon-intron structure diagrams of the A. thaliana AtABF1, AtABF2, AtABF3, and AtABF4 genes and the A. chinensis AcABF genes, with green denoting the UTR, yellow showing the CDS, and the line segment in the center indicating the intron. The ruler represents the length of the genes.
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Figure 5. Cis-acting elements of A. chinensis ABF genes. (a) The number of cis-acting elements of each ABF gene and the numbers in the heatmap boxes indicate the number of different elements in these AcABFs; (b) the position of each cis-acting element.
Figure 5. Cis-acting elements of A. chinensis ABF genes. (a) The number of cis-acting elements of each ABF gene and the numbers in the heatmap boxes indicate the number of different elements in these AcABFs; (b) the position of each cis-acting element.
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Figure 6. Chromosomal localization and covariance map of the ABF gene in A. chinensis. (a) Chromosomal localization map of the ABF gene in A. chinensis. (b) Covariance map between different species of kiwifruit, rice, A. thaliana, and apple. The gray lines denote the duplicated blocks, whereas the blue lines denote the covariant ABF gene pairs.
Figure 6. Chromosomal localization and covariance map of the ABF gene in A. chinensis. (a) Chromosomal localization map of the ABF gene in A. chinensis. (b) Covariance map between different species of kiwifruit, rice, A. thaliana, and apple. The gray lines denote the duplicated blocks, whereas the blue lines denote the covariant ABF gene pairs.
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Figure 7. GO enrichment analysis plot of the AcABF genes. (a) GO functional enrichment of the kiwifruit ABF gene; from the inside out, the 1st circle bar indicates the ratio of the number of genes with significant AcABF differences enriched with the same GO term to the total number of AcABF genes; the 2nd circle indicates the number of AcABF genes enriched with differences in upregulation and downregulation of the GO term, with green denoting upregulation and yellow denoting downregulation; the 3rd circle heatmap represents the total number of genes enriched with the corresponding GO term; and the 4th circle represents the GO number, and different classifications are indicated by different colors. (b) The name of the GO corresponding to the GO ID.
Figure 7. GO enrichment analysis plot of the AcABF genes. (a) GO functional enrichment of the kiwifruit ABF gene; from the inside out, the 1st circle bar indicates the ratio of the number of genes with significant AcABF differences enriched with the same GO term to the total number of AcABF genes; the 2nd circle indicates the number of AcABF genes enriched with differences in upregulation and downregulation of the GO term, with green denoting upregulation and yellow denoting downregulation; the 3rd circle heatmap represents the total number of genes enriched with the corresponding GO term; and the 4th circle represents the GO number, and different classifications are indicated by different colors. (b) The name of the GO corresponding to the GO ID.
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Figure 8. Comparative graphs of the physiological indices of A. chinensis histocultured seedlings in the control and drought stress-treated groups. (a) ABA; (b) ABA-ald (abscisic aldehyde); (c) ABA-GE (abscisic acid glucose ester); (d) ACC (desmotropic enzyme); CK: control group; T: treatment group; p-value obtained through hypothesis testing; ** denotes a p-value < 0.01.
Figure 8. Comparative graphs of the physiological indices of A. chinensis histocultured seedlings in the control and drought stress-treated groups. (a) ABA; (b) ABA-ald (abscisic aldehyde); (c) ABA-GE (abscisic acid glucose ester); (d) ACC (desmotropic enzyme); CK: control group; T: treatment group; p-value obtained through hypothesis testing; ** denotes a p-value < 0.01.
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Figure 9. KEGG signaling pathway map of ABF (AcABF2, AcABF3, AcABF8, AcABF9, and AcABF10) genes. Carotenoid biosynthesis, abscisic acid (ABA); PYR/PYL: ABA receptor; PP2C: phosphatases of type 2C; SnPK2: related protein kinase 2. Two solid gray lines represent the cell membrane, solid arrows represent activation, dashed arrows represent indirect effects, dashed arrows represent state changes, straight lines represent binding, circles represent chemical compound, DNA and other molecule, and dashed lines represent inhibition. The four rectangles represent the complex.
Figure 9. KEGG signaling pathway map of ABF (AcABF2, AcABF3, AcABF8, AcABF9, and AcABF10) genes. Carotenoid biosynthesis, abscisic acid (ABA); PYR/PYL: ABA receptor; PP2C: phosphatases of type 2C; SnPK2: related protein kinase 2. Two solid gray lines represent the cell membrane, solid arrows represent activation, dashed arrows represent indirect effects, dashed arrows represent state changes, straight lines represent binding, circles represent chemical compound, DNA and other molecule, and dashed lines represent inhibition. The four rectangles represent the complex.
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Figure 10. Heatmap of AcABF gene expression under drought stress and qRT-PCR results for five AcABF genes. (a) Heatmap of AcABF gene expression under drought stress; (b) qRT-PCR results of five AcABF genes; CK denotes the control; and T denotes drought stress for 72 h. **: p < 0.01.
Figure 10. Heatmap of AcABF gene expression under drought stress and qRT-PCR results for five AcABF genes. (a) Heatmap of AcABF gene expression under drought stress; (b) qRT-PCR results of five AcABF genes; CK denotes the control; and T denotes drought stress for 72 h. **: p < 0.01.
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Figure 11. Putative map of the ABA signaling model involving ABF (AcABF2, AcABF3, AcABF8, AcABF9, and AcABF10) genes. ABA: abscisic acid; PYR/PYL: ABA receptor; PP2C: phosphatases of type 2C; SnPK2: sucrose nonfermenting 1-related protein kinase 2.
Figure 11. Putative map of the ABA signaling model involving ABF (AcABF2, AcABF3, AcABF8, AcABF9, and AcABF10) genes. ABA: abscisic acid; PYR/PYL: ABA receptor; PP2C: phosphatases of type 2C; SnPK2: sucrose nonfermenting 1-related protein kinase 2.
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MDPI and ACS Style

Wang, H.; Zi, Y.; Rong, X.; Zhang, Q.; Nie, L.; Wang, J.; Ren, H.; Zhang, H.; Liu, X. Expression Analysis of the ABF Gene Family in Actinidia chinensis Under Drought Stress and the Response Mechanism to Abscisic Acid. Horticulturae 2025, 11, 715. https://doi.org/10.3390/horticulturae11070715

AMA Style

Wang H, Zi Y, Rong X, Zhang Q, Nie L, Wang J, Ren H, Zhang H, Liu X. Expression Analysis of the ABF Gene Family in Actinidia chinensis Under Drought Stress and the Response Mechanism to Abscisic Acid. Horticulturae. 2025; 11(7):715. https://doi.org/10.3390/horticulturae11070715

Chicago/Turabian Style

Wang, Haoyu, Yinqiang Zi, Xu Rong, Qian Zhang, Lili Nie, Jie Wang, Hailin Ren, Hanyao Zhang, and Xiaozhen Liu. 2025. "Expression Analysis of the ABF Gene Family in Actinidia chinensis Under Drought Stress and the Response Mechanism to Abscisic Acid" Horticulturae 11, no. 7: 715. https://doi.org/10.3390/horticulturae11070715

APA Style

Wang, H., Zi, Y., Rong, X., Zhang, Q., Nie, L., Wang, J., Ren, H., Zhang, H., & Liu, X. (2025). Expression Analysis of the ABF Gene Family in Actinidia chinensis Under Drought Stress and the Response Mechanism to Abscisic Acid. Horticulturae, 11(7), 715. https://doi.org/10.3390/horticulturae11070715

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