Next Article in Journal
Nutritional and Phenolic Profile of Early and Late Harvested Amaranth Leaves Grown Under Cultivated Conditions
Previous Article in Journal
Farmers’ Knowledge and Management Practices of Fall Armyworm, Spodoptera frugiperda (J.E. Smith) in Benin, West Africa
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Agriculture
Volume 10
Issue 10
10.3390/agriculture10100429
agriculture-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Comprehensive Genomic Characterization and Expression Analysis of the Lipoxygenase Gene Family in Watermelon under Hormonal Treatments

by
Jianping Liu
1,2,
Yong Zhou
2,
Jingwen Li
1,
Feng Wang
3 and
Youxin Yang
1,*
1
Jiangxi Key Laboratory for Postharvest Technology and Nondestructive Testing of Fruits & Vegetables, Collaborative Innovation Center of Post-Harvest Key Technology and Quality Safety of Fruits and Vegetables, College of Agronomy, Jiangxi Agricultural University, Nanchang 330045, China
2
College of Bioscience and Bioengineering, Jiangxi Agricultural University, Nanchang 330045, China
3
College of Horticulture, Shenyang Agricultural University, Shenyang 110866, China
*
Author to whom correspondence should be addressed.
Agriculture 2020, 10(10), 429; https://doi.org/10.3390/agriculture10100429
Submission received: 2 August 2020 / Revised: 18 September 2020 / Accepted: 21 September 2020 / Published: 25 September 2020
Browse Figures
Versions Notes

Abstract

:
Lipoxygenases (LOXs) are non-haem iron-containing dioxygenases and play vital roles in a variety of plant biological processes. Here, we first carried out the genome-wide identification of LOX genes in watermelon. A total of 16 LOX genes were identified, which could be classified into two categories according to phylogenetic analysis: the 9-LOXs (ClLOX1–4, 12, and 15) and 13-LOXs (ClLOX5–11, 13, 14, and 16). Furthermore, the protein structures, intrachromosomal distributions, and gene structures were thoroughly analyzed. Cis-element analysis of the promoter regions indicated that the expression of ClLOX genes may be influenced by stress and plant hormones. Bioinformatic and expression analyses revealed that the expression of ClLOX genes is tissue-specific and hormone-responsive. The detected LOX genes exhibited distinctive expression patterns in various tissues. Different ClLOX genes showed different responses to methyl jasmonate (MeJA), salicylic acid (SA), and ethylene (ET) treatments, particularly ClLOX7, which exhibited the most active response to the above treatments. This study provides valuable information for a better understanding of the functions of LOX genes and further exploration of the LOX gene family in watermelon.

1. Introduction

Lipoxygenases (LOXs; EC 1.13.11.12) belong to a family of non-haem iron-containing dioxygenases that are widely present in plants, animals, fungi, and even in bacteria [1,2,3,4]. They can catalyze the oxidation of polyunsaturated fatty acids (PUFAs), such as linoleic acid (LA) and α-linolenic acid (α-LeA), into unsaturated fatty acid hydroperoxides [2,5]. In plants, LOX-mediated peroxidation of PUFAs undergoes a series of secondary reactions involving several multigene enzyme families, such as Allene oxide synthase (AOS), hydroperoxide lyase (HPL), divinyl ether synthase (DES), and allene oxide cyclase (AOC), and finally produces a large number of biologically active compounds such as jasmonic acid (JA) and its related chemical compounds [1,6,7].
Plant LOXs have a highly conserved lipoxygenase domain at the C-terminus and a PLAT/LH2 (polycystin-1, lipoxygenase, α-toxin domain, or lipoxygenase homology) domain at the N-terminus [8]. According to whether the substrate is oxygenated at carbon atom 9 or 13 of the fatty acid hydrocarbon backbone, plant LOXs are generally divided into two categories of 9-LOXs and 13-LOXs [2]. In addition, based on their primary structure and overall sequence similarity, plant LOXs can also be classified into two subfamilies: type I and type II. Type I LOXs have relatively higher sequence similarities with each other than type II LOXs and are lack of plastid transit peptide [2,9]. Type II exclusively comprises 13-LOXs, and all the proteins harbor an extra chloroplast transit peptide at the N-terminus [10,11].
By genome-wide analysis, previous studies have identified six LOX family genes in Arabidopsis [12], eight in Tartary buckwheat [10], eight in pepper [13], 11 in either tea plant [14] or radish [15], 13 in maize [16], 14 in either rice [17] or tomato [18], 18 in either grape [19] or melon [20], 20 in poplar [11], and 23 in either cucumber [21] or pear [22]. In addition, many LOX genes have been cloned and functionally characterized to be involved in various growth and developmental processes in plants. For example, lox3 lox4 double mutants were male sterile and developed more inflorescence shoots and flowers, suggesting that they are essential for male fertility and flower development in Arabidopsis [23]. Down-regulation of a rice LOX gene reduced the co-oxidation of β-carotene in carotenoid-enriched transgenic rice seeds during storage [24]. Moreover, some LOX members were found to be associated with resistance against various abiotic and biotic stresses. For example, silencing of pepper CaLOX2 gene reduced jasmonate accumulation and caused higher susceptibility to thrips feeding [25]. Overexpression of persimmon (Diospyros kaki) DkLOX3 gene in Arabidopsis contributed to higher resistance against various abiotic stresses, including osmotic stress, high salinity, and drought, as well as biotic stresses including Pseudomonas syringae pv. tomato DC3000 and Botrytis cinerea [26,27].
Considering that LOX family members have important functions in different developmental processes and various stress responses as mentioned above, we conducted a genome-wide analysis of LOX genes in watermelon genome and systematically analyzed their phylogenetic relationships, protein structures, intrachromosomal localizations, and exon-intron arrangements. In addition, the cis-element analysis of the promoter regions was performed, and the expression patterns of watermelon LOX genes in different tissues and in response to various hormonal treatments were also determined. The results may lay a foundation for further elucidating the functions of the LOX genes and facilitate the molecular breeding of watermelon.

2. Materials and Methods

2.1. Identification of LOX Gene Family Members in Watermelon

To identify all the possible LOX genes in watermelon, the HMM (Hidden Markov Model) profile of the LOX domain (PF00305) was downloaded from the Pfam database (http://pfam.xfam.org/) and searched against the watermelon (97103) v1 proteome (http://cucurbitgenomics.org/organism/1) using the HMMER program with default parameters. Subsequently, the full-length LOX protein sequences in Arabidopsis and rice were downloaded according to a previous study [17], and used as queries to search against the watermelon (Citrullus lanatus subsp. vulgaris cv. 97103) v1 proteome with the BLASTP program. The resulting sequences were further verified by SMART (http://smart.embl-heidelberg.de/) and Pfam to confirm the presence of both the LOX and PLAT/LH2 domains. Several redundant sequences were removed for not having the complete domain or shortness.

2.2. Analysis of Protein Properties, Phylogenetic Tree and Conserved Motifs

The isoelectric point (pI), molecular weight (MW) and grand average of hydropathicity (GRAVY) of watermelon LOX proteins were calculated by the ProtParam tool in ExPASy (https://web.expasy.org/protparam/). The subcellular localization of each member of watermelon LOX proteins was predicted using the ProtComp server (Version 9.0, New York, NY, USA) http://linux1.softberry.com/berry.phtml). Multiple sequence alignment was carried out by MAFFT (https://www.ebi.ac.uk/Tools/msa/mafft/) using the full-length sequences of LOX proteins from watermelon and other plant species, including tomato [18], pepper [13], Arabidopsis, and rice [17]. A phylogenetic tree was constructed with the MEGA 7.0 using the neighbor-joining (NJ) method with a bootstrap value of 1000. The conserved motifs of watermelon LOX proteins were identified using the MEME tool (http://meme-suite.org/tools/meme), and the parameter settings were set as follows: the number of motifs was 10, and the width range was 6–50. The MEME results were illustrated with the TBtools program [28].

2.3. Analysis of the Gene Structure and Putative Cis-Acting Regulatory Elements

The GSDS tool (Gene Structure Display Server, http://gsds.cbi.pku.edu.cn/) was employed to examine the gene structures of watermelon LOX genes by comparing their sequences of coding sequence (CDS) and corresponding genomic DNA (gDNA). To identify the potential stress- and hormone-related cis-elements, the 2000-bp DNA sequences of ATG site of watermelon LOX genes were obtained from the watermelon (97103) v1 genome database (http://cucurbitgenomics.org/organism/1) and analyzed by the PlantCARE server (http://bioinformatics.psb.ugent.be/webtools/plantcare/html/).

2.4. Chromosome Mapping, Duplication and Synteny Analysis

The chromosomal information of watermelon LOX genes was downloaded from the watermelon genome database and the LOX genes were mapped to chromosomes with the MapChart software. Duplication analysis between the watermelon LOX genes and synteny analysis of LOX genes between watermelon and Arabidopsis were conducted with the MCScanX software (Athens, GA, USA) (http://chibba.pgml.uga.edu/mcscan2/) by referring to a previous report [29].

2.5. Expression Analysis of Watermelon LOX Genes Based on RNA-Seq Data

The RNA-seq data of the flesh and rind at 10, 18, 26, and 34 days after pollination (DAP) were obtained, and the expression annotation was performed as previously described [6,30]. FPKM (fragments per kilobase of exon model per million mapped reads) values of watermelon LOX genes were log2-transformed, and then the TBtools program was employed to visualize the expression values.

2.6. Plant Materials and Growth Conditions

Watermelon (Citrullus lanatus L. cv. Xinong 8) seeds were sown in pots containing nutritional soil within a greenhouse under the conditions of 25 °C/19 °C (12 h/12 h). For analysis of tissue-specific expression patterns, various tissues including leaves, roots, stems, flowers, and fruit were harvested from 2-month-old watermelon plants. For various hormone treatments, four-leaf stage watermelon seedlings were treated with 100 µM methyl jasmonate (MeJA), 1 mM salicylic acid (SA), and 500 μM ethylene (ET) by spraying according to our previous study [30]. Then, the leaves and roots were harvested from treated seedlings at 0, 1, 3, 9, and 24 h post-treatment with three biological triplicates. All of the samples were rapidly frozen in liquid nitrogen and stored at −80 °C until use.

2.7. RNA Extraction and Quantitative Real-Time PCR (qRT-PCR) Analysis

Total RNA was extracted with the total RNA Miniprep Kit (Axygen Biosciences, Union City, CA, USA) following the manufacturers’ protocol. The RNA (1 µg) was reverse-transcribed using the ReverTra Ace qPCR-RT Kit (TOYOBO, Osaka, Japan) for the synthesis of cDNA. qRT-PCR was performed on the iCycler iQTM Real-time PCR Detection System (Bio-Rad, Hercules, CA, USA) in three independent biological replicates. The primers used are described in Supplementary Table S1. Watermelon β-actin gene (Cla007792) was used as an internal control, and the relative expression was analyzed using by the 2−ΔΔCt method [31].

3. Results

3.1. Identification of LOX Genes in Watermelon

By HMMER search and BLASTP, a total of 19 LOX genes were identified in watermelon (C. lanatus) genome, three of which were removed for shortness and not having the complete domain of LOX as tested by SMART and Pfam. Finally, the 16 LOX genes were denoted as ClLOX1–16 in an ascending order of the corresponding chromosomes (Table 1). The gDNA and CDS lengths of the ClLOX family genes varied from 2913 to 9824 bp and from 1686 to 2787 bp, respectively, encoding proteins ranging from 561 to 928 amino acids (aa) in length with an average length of 810.06 aa. In addition, the calculated MW, pI, and GRAVY values varied from 85.95 to 105.04 kDa, from 5.13 to 8.83, and from −0.581 to −0.187, respectively (Table 1). The subcellular localization analysis showed that the watermelon LOX proteins were located in cytoplasm and chloroplast (Table 1).

3.2. Evolutionary Relationship among LOX Family Members in Various Plant Species

To reveal the phylogenetic relationships of LOX family members in watermelon and other plant species, a phylogenetic tree was constructed based on the protein sequences of watermelon, pepper [13], tomato [18], Arabidopsis, and rice [17]. As a result, these LOX proteins could be clearly divided into two categories of 9-LOXs and 13-LOXs. Among the watermelon LOX proteins, six members (ClLOX1–4, 12, and 15) were grouped into the 9-LOX category, while other 10 members fell into the 13-LOX category (Figure 1). It is worth noting that ClLOX1–4 were clustered in the 9-LOX category, while ClLOX5–11 and ClLOX13 were clustered together in the 13-LOX category (Figure 1), suggesting that the ClLOX proteins may be evolutionarily conserved.

3.3. Characterization and Conserved Domain Analysis of Watermelon LOX Proteins

To determine the evolutionarily conserved domains, the full-length amino acid sequences of ClLOX proteins were submitted to pfam and SMART tools. The results showed that all watermelon 9-LOXs and 13-LOXs harbored both a conserved LH2/PLAT and a LOX domain, while ClLOX9 seemed to have a truncated LOX domain (Figure 2A,B).
The structures of the ClLOX proteins were further examined by using the MEME server. A total of 10 motifs (designated as motif 1–10) were identified for the 16 ClLOX proteins (Figure 2C). Amongst them, motifs 1–9 corresponded to the LOX domain, while motif 10 was part of the LH2/PLAT domain (Supplementary Figure S1). Motif 1 included a representative motif of 38 amino acids [His-(X)4-His-(X)4-His-(X)17-His-(X)8-His] with five conserved His (H) residues, which was demonstrated to play a vital role in iron binding and is necessary for enzyme stability and activity [5,32,33]. The 10 motifs were widely present in all ClLOX proteins, and their distributions exhibited certain degrees of specificity (Figure 2). The majority of ClLOX proteins harbored motif 1, except for ClLOX6 (Figure 2C). Besides, some other ClLOX proteins were also lack of certain conserved motifs. For example, motif 4, motif 5, motif 6, and motif 9 were absent in ClLOX13, while motif 10 was not found in ClLOX4. In addition, ClLOX1 and ClLOX2 had an additional motif 8 in their N-terminus (Figure 2C). These differences in motif arrangement may account for the functional differentiation among LOX proteins in watermelon.
To further characterize the structures of watermelon LOX proteins, all full-length ClLOX protein sequences were aligned by MAFFT, and the representative motif of 38 amino acids was shown in Figure S2. The watermelon 13-LOXs had a conserved F residue that is indicative of the 13-LOX activity of LOX enzymes, while the 9-LOXs had V/H/L in the corresponding position (Supplementary Figure S2).

3.4. Intrachromosomal Localization and Structural Analysis of Watermelon LOX Genes

The 16 ClLOX genes were mapped on five of the eleven chromosomes in watermelon genome, and the number of genes on each chromosome was highly uneven (Figure 3). Chromosome 2 comprised the largest number of ClLOX genes (11 genes). Chromosome 9 included two ClLOX genes, while each of chromosomes 6, 7, and 11 only had one ClLOX gene (Figure 3).
Further, we carried out a synteny analysis of LOX genes between watermelon and Arabidopsis. All Arabidopsis LOX genes had syntenic copies in watermelon (Supplementary Figure S3), and these syntenic relationships may originate from whole genome triplication or segmental duplication events [15]. To further trace the evolutionary history of ClLOX genes, we investigated the duplication information of them using MCScanX. The results showed that a total of 10 ClLOX genes (ClLOX1, 2, 3–10) could be determined as tandemly duplicated genes.
The structural features of ClLOX genes were examined by the GSDS tool. Generally, all ClLOX genes harbored introns in their genomic sequences, and the intron number varied from two to eight (Figure 4). All 9-LOX genes (6 out of 9) contained eight introns. Most of the 13-LOX genes comprised 7–8 introns, except for ClLOX7, ClLOX10, and ClLOX14, which had 6, 5, and 6 introns, respectively (Figure 4).

3.5. Cis-Element Analysis in the Promoter Regions of ClLOX Genes

To reveal the possible transcriptional regulation patterns of the ClLOX genes, the 2.0-kb sequence upstream of the ATG site of ClLOX genes was retrieved and analyzed by using the PlantCARE program. A total of 15 kinds of cis-elements involved in responses to stresses and plant hormones were identified, and all ClLOX genes contained 2–8 kinds of cis-elements in their promoter regions, with the exception of ClLOX7 (Figure 5). Among the stress- and hormone-related cis-elements, anaerobic induction element (ARE) and ET responsive element (ERE) were the most frequently detected in ClLOX genes. In addition, 1, 3, 3, 4, 5, and 5 ClLOX genes had the dehydration-responsive element (DRE), low temperature responsive element (LTR), defense and stress-responsive elements (TC-rich repeats), MYB binding site involved in drought and stress (MBS), WRKY binding site (W-box), and wound-responsive element (WUN-motif), respectively (Figure 5), implying the possible roles of ClLOX genes in responses to various stresses. Besides the ERE element, seven other important hormone-related cis-elements were also widely identified, including ABRE, CGTCA-motif, TCA-element, AuxRR-core, TGA-element, P-box, and GARE-motif, suggesting that the ClLOX genes may be regulated by various plant hormones. Notably, over half of ClLOX genes (nine out of 16) contained the TCA-element in their promoters, and ABA responsive element (ABRE), MeJA responsive element (CGTCA-motif), auxin-responsive element (AuxRR-core and TGA-element), and gibberellin responsive element (P-box and GARE-motif) were found in the promoter regions of 7, 5, 4, and 6 ClLOX genes, respectively (Figure 5).

3.6. Expression Analysis of ClLOX Genes in Different Tissues and during Fruit Development

Four ClLOX genes (one from 9-LOXs and three from 13-LOXs) were selected to examine their expression levels in various tissues, including leaves, roots, stems, flowers, and fruit. The qRT-PCR results indicated that some ClLOX genes may have tissue-specific expression patterns. For example, ClLOX14 was highly expressed in fruit; ClLOX4 and ClLOX7 exhibited the most abundant transcripts in flowers; while ClLOX8 showed evident expression specificity in roots (Figure 6). We further determined the expression patterns of ClLOX genes during fruit development in watermelon based on RNA-seq data by referring to our previous study [6]. During the development of flesh, ClLOX5 and ClLOX15 showed decreases in transcript levels. During rind development, ClLOX4, ClLOX5, and ClLOX16 displayed increases in transcripts at some time points, particularly at 26 DAP (Supplementary Figure S4).

3.7. Expression Analysis of Several Watermelon ClLOX Genes in Response to JA, SA and ET Treatment

Considering that the ClLOX genes harbor a large number of hormone-related cis-elements, qRT-PCR was carried out to investigate the expression patterns of selected ClLOX genes under JA, SA, and ET treatments. Upon JA treatment, the expression levels of ClLOX7, ClLOX12, and ClLOX14 showed notable increases in both the leaf and root, with the most significant increases being observed for ClLOX7, suggesting that ClLOX7 plays a primary role in JA signaling in leaves and roots (Figure 7A,B). However, ClLOX4 and ClLOX16 showed different expression patterns in leaves and roots under JA treatment. The expression of ClLOX4 observably decreased in leaves but gradually increased and reached the highest level at 9 h in roots (Figure 7A,B). For ClLOX16, the expression increased and peaked at 24 h in leaves, while exhibited a significant decrease in roots at 3 h (Figure 7A,B). Upon SA treatment, ClLOX7 and ClLOX16 showed similar expression patterns, and their transcripts dramatically increased and peaked at 3 h, while the expression of ClLOX14 showed remarkable declines at certain time points (Figure 7C). Upon ET treatment, the expression of ClLOX7 and ClLOX16 showed significant increases, while that of ClLOX4 and ClLOX12 displayed significant decreases at certain time points (Figure 7D). In addition, the expression of ClLOX14 was observably induced at earlier time points (1 h), but showed sharp decreases thereafter (Figure 7D). These results indicated that ClLOX genes may be involved in diverse hormonal responses.

4. Discussion

LOX proteins are widely present in plants, and are generally encoded by a multigene family. In this study, a total of 16 LOX proteins were identified in watermelon through HMMER combined with BLASTP search (Table 1), and several proteins possessing either one LOX domain or the PLAT/LH2 domain were excluded based on the criteria in previous reports [11,13]. Watermelon has a comparatively larger number of LOX family members relative to other plant species, such as Arabidopsis (six members) [12], pepper (eight members) [13], tea plant (11 members) [14], tomato (14 members) [18], and melon (18 members) [20], and the number of LOX genes in these plants is not proportional to their genome sizes. Notably, 11 out of the 16 ClLOX genes were located on chromosome 2 and formed two distinct tandem duplicate gene clusters (Figure 3). Moreover, over half of the ClLOX genes (10 in 16) were identified as tandemly duplicated genes, indicating that tandem duplication events are the main driving force for the evolution of ClLOX genes. This feature has also been found in some other plants, such as poplar [11], maize [16], tomato [18], cucumber [34], and radish [15]. In addition, according to the collinear module of watermelon and Arabidopsis, all of the six AtLOX genes have syntenic copies in ClLOX genes (Supplementary Figure S3). The larger number of AtLOX-ClLOX orthologous events indicates that ClLOX genes may have similar structure and function to AtLOX genes.
Through a phylogenetic analysis of the LOX gene family in watermelon and other plant species, LOX family members can be divided into the categories of 9-LOXs and 13-LOXs (Figure 1), which is in accordance with the classification of LOXs in previous reports [2,7,13]. All the watermelon 13-LOX members contain the F residue at the active site (Figure S2), which is indicative of the 13-LOX activity of LOX enzymes [35,36]. However, the 9-LOXs had V/H/L in the corresponding position instead (Figure S2). The conserved V residue associated with 9-LOX activity is a characteristic of LOX enzymes, while some 9-LOXs possess no V residue at the position [37,38,39]. In addition, the analysis of conserved motif distribution and exon-intron arrangement further supported the phylogenetic results. The LOXs clustered together tended to have similar conserved motif distributions and structural features (Figure 2 and Figure 4). However, some phylogenetically related ClLOX genes had similar exon/intron structures but variable numbers of introns, such as ClLOX12 and ClLOX13, ClLOX17 and ClLOX19 (Figure 4), suggesting that gain or loss of introns may occur during the evolution of ClLOX genes, which may be responsible for their indispensable roles in watermelon.
Previous studies have shown that some LOX genes have distinctive expression patterns, which may provide important clues for understanding their physiological functions. For example, over half of the PtLOX genes were found to be preferentially expressed in mature leaves and male catkins [11]. Most of the GhLOX genes were expressed in vegetative tissues, while several GhLOX genes were only expressed in specific tissues, such as GhLOX4, GhLOX5, and GhLOX15 in root, GhLOX7 in stem, and GhLOX17 and GhLOX19 in stigma [32]. In the present study, the identified ClLOX genes also displayed significantly higher expression only in specific tissues, such as ClLOX14 in fruit, ClLOX4 and ClLOX7 in flowers, and ClLOX8 in roots (Figure 6), suggesting their specific roles in these tissues. In addition, two tandemly duplicated genes, ClLOX7 and ClLOX8, exhibited diverse tissue expression patterns (Figure 6), implying that they are functionally distinctive and have undergone non-functionalization, sub-functionalization, or neofunctionalization [40,41]. In addition, several ClLOX genes showed decreases in transcript abundance during fruit development (Supplementary Figure S4), and similar results were also found in kiwifruit [42], grape [19], melon [20], and tomato [18,43]. The higher expression levels of these LOX genes indicate that plants may require the LOX activity for cell division and fruit enlargement during early developmental periods. Instead, ClLOX4, ClLOX5, and ClLOX16 showed increases in transcripts during the late stage of rind development, implying their regulatory roles in fruit ripening. Previous reports have revealed that the LOX activity is associated with membrane degradation during fruit ripening, and ethyl and butyl acetates would increase with fruit ripening [20,44]. Therefore, the continuous increase in the expression of LOX genes during fruit development may be associated with cell degradation and senescence during fruit ripening.
The LOX pathway is involved in the early steps of plant responses to pathogen and insect attacks. The analysis of cis-elements uncovered many hormone-related cis-elements in the promoter regions of the ClLOX genes (Figure 5). Therefore, we determined the expression profiles of some selected ClLOX genes upon different plant hormone treatments. Under JA treatment, the expression of all the genes was altered, particularly ClLOX7, which exhibited more dramatic increases of expression in both leaves and roots relative to ClLOX genes (Figure 7A,B). ClLOX7 is orthologous to AtLOX2 in the 13-LOX group (Figure 1), both of which were localized in chloroplasts (Table 1). Therefore, compared with other ClLOX genes, ClLOX7 might play a primary role similar to that of AtLOX2, which can provide linolenic acid hydroperoxide substrates for JA biosynthesis in vivo [45]. JA, SA, and ET are three main defense-associated phytohormones that mediate signal transduction to combat attackers such as pathogens and herbivorous insects, and the SA- and ET/JA-mediated defense response pathways were reported to act antagonistically, synergistically, or additively [46,47,48]. In this study, the selected ClLOX genes were also found to be regulated in response to SA and ET treatments (Figure 7C,D). Our previous reports have shown that other oxylipin pathway genes, such as ClAOCs, ClAOS and ClHPLs, are also regulated in response to JA, SA, and ET, which may play important roles in watermelon defense against root-knot nematode (RKN) infection [6,30]. The roles of LOXs in the defense against pathogens and pests might be associated with the synthesis of a number of compounds from the oxylipin pathway [1,7]. For example, OsLOX1 could lead to the production of more JA, (Z)-3-hexenal, and colneleic acid after brown plant hopper (BPH) feeding, and transgenic rice plants with enhanced OsLOX1 expression were more resistant to BPH attack [49]. Tea plant CsLOX1 was induced in response to feeding by the tea green leafhopper, and the expression profile showed a clear association with the emission pattern of LOX-derived volatiles [50]. ZmLOX10 provides substrate to several LOX branches and produces a series of 13-oxylipin products, and the zmlox10 plants were unable to produce green leaf volatiles (GLVs) and JA, resulting in a dramatic decline in herbivore-induced plant volatiles and attractiveness to parasitoid wasps [51,52]. A recent study has revealed that GLVs and JA contribute to maize susceptibility to Colletotrichum graminicola due to the suppression of SA-related defense [53]. Hence, the ClLOX genes may participate in the protection of plants from biotic stresses by catalyzing the synthesis of some oxylipins through the regulation of the SA- and ET/JA-mediated defense response pathways. In addition, some DRE and ABRE and ERE cis-elements were found in the promoters of LOXs, suggesting that these LOXs may participate in watermelon defense against abiotic stress. A recent report has revealed that tomato LOXs were up-regulated or down-regulated in response to heat, salt, or drought stress [54]. In future work, we will focus on the functions of watermelon LOX genes in defense against abiotic stress.

5. Conclusions

In summary, a total of 16 LOX genes were identified in watermelon, which could be divided into two categories: 9-LOXs (ClLOX1–4, 12, and 15) and 13-LOXs (ClLOX5–11, 13, 14, and 16). Their phylogenetic relationships, protein structures, intrachromosomal distributions, gene structures, and cis-element compositions in the promoters were thoroughly analyzed in this work. The results improve our understanding of the LOX gene family in watermelon. In addition, the expression analysis of some selected ClLOX genes showed that their expression is tissue-specific as well as hormone-responsive. These findings may expand the understanding of the functions of ClLOX genes and lay a foundation to select candidate genes for watermelon genetic improvement.

Supplementary Materials

The following are available online at https://www.mdpi.com/2077-0472/10/10/429/s1. Figure S1. Logo of 10 motifs of watermelon LOX proteins by MEME. Figure S2. Multiple sequence alignments of the representative 38 amino acid motif of watermelon LOX proteins. The representative 38 amino acid motif is boxed with purple. The five essential His residues involved in the binding of the iron atom in the active site are denoted by asterisks. The residues indicative of LOX enzymes with 9- or 13-LOX activity are boxed with red. Figure S3. Collinear relationships of LOX genes in watermelon and Arabidopsis. Figure S4. Expression patterns of ClLOX genes during the development of flesh and rind at different stages. The expression levels are indicated as log2-based FPKM+1 values. DAP, days after pollination. Table S1. Primers sequences used in qRT-PCR. Table S2. LOX family proteins from different plant species used in this study.

Author Contributions

Data curation, J.L. (Jianping Liu), Y.Z., J.L. (Jingwen Li), and Y.Y.; formal analysis, J.L. (Jianping Liu); funding acquisition, Y.Y. and F.W.; methodology, J.L. (Jingwen Li) and Y.Z.; resources, J.L. (Jianping Liu), Y.Z., and Y.Y.; software, J.L. (Jingwen Li) and F.W.; writing—original draft, J.L. (Jianping Liu) and Y.Z.; writing—review and editing, Y.Y. and F.W. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the National Natural Science Foundation of China (31560572 and 31801904), and the Foundation of Jiangxi Educational Committee (GJJ190219), the Liaoning Revitalization Talents Program (XLYC1807020), the Doctoral Research Foundation of Liaoning Province (20180540094), the Innovative Talent Support Program for the Universities in Liaoning Province, the Young and Middle-aged Science and Technology Innovation Talents Program in Shenyang (RC200449).

Conflicts of Interest

The authors declare that they have no conflict of interest.

References

  1. Porta, H.; Rocha-Sosa, M. Plant lipoxygenases. Physiological and molecular features. Plant Physiol. 2002, 130, 15–21. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  2. Feussner, I.; Wasternack, C. The lipoxygenase pathway. Annu. Rev. Plant Biol. 2002, 53, 275–297. [Google Scholar] [CrossRef] [PubMed]
  3. Wennman, A.; Oliw, E.H.; Karkehabadi, S.; Chen, Y. Crystal structure of manganese lipoxygenase of the rice blast fungus Magnaporthe oryzae. J. Biol. Chem. 2016, 291, 8130–8139. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  4. Banthiya, S.; Kalms, J.; Yoga, E.G.; Ivanov, I.; Carpena, X.; Hamberg, M.; Kuhn, H.; Scheerer, P. Structural and functional basis of phospholipid oxygenase activity of bacterial lipoxygenase from Pseudomonas aeruginosa. Biochim. Biophys. Acta 2016, 1861, 1681–1692. [Google Scholar] [CrossRef]
  5. Song, H.; Wang, P.; Li, C.; Han, S.; Lopez-Baltazar, J.; Zhang, X.; Wang, X. Identification of lipoxygenase (LOX) genes from legumes and their responses in wild type and cultivated peanut upon Aspergillus flavus infection. Sci. Rep. 2016, 6, 35245. [Google Scholar] [CrossRef] [Green Version]
  6. Zhou, Y.; Guang, Y.; Li, J.; Wang, F.; Ahammed, G.J.; Yang, Y. The CYP74 gene family in watermelon: Genome-wide identification and expression profiling under hormonal stress and root-knot nematode infection. Agronomy 2019, 9, 872. [Google Scholar] [CrossRef] [Green Version]
  7. Viswanath, K.K.; Varakumar, P.; Pamuru, R.R.; Basha, S.J.; Mehta, S.; Rao, A.D. Plant lipoxygenases and their role in plant physiology. J. Plant. Biol. 2020, 63, 83–95. [Google Scholar] [CrossRef]
  8. Tolley, J.P.; Nagashima, Y.; Gorman, Z.; Kolomiets, M.V.; Koiwa, H. Isoform-specific subcellular localization of Zea mays lipoxygenases and oxo-phytodienoate reductase 2. Plant Gene 2018, 13, 36–41. [Google Scholar] [CrossRef]
  9. Andreou, A.; Feussner, I. Lipoxygenases—Structure and reaction mechanism. Phytochemistry 2009, 70, 1504–1510. [Google Scholar] [CrossRef]
  10. Ji, Q.; Zhang, T.; Zhang, D.; Lv, S.; Tan, A. Genome-wide identification and expression analysis of lipoxygenase genes in Tartary buckwheat. Biotechnol. Biotechnol. Equip. 2020, 34, 273–286. [Google Scholar] [CrossRef] [Green Version]
  11. Chen, Z.; Chen, X.; Yan, H.; Li, W.; Li, Y.; Cai, R.; Xiang, Y. The lipoxygenase gene family in poplar: Identification, classification, and expression in response to MeJA treatment. PLoS ONE 2015, 10, e0125526. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  12. Bannenberg, G.; Martinez, M.; Hamberg, M.; Castresana, C. Diversity of the enzymatic activity in the lipoxygenase gene family of Arabidopsis thaliana. Lipids 2009, 44, 85–95. [Google Scholar] [CrossRef] [PubMed]
  13. Sarde, S.J.; Kumar, A.; Remme, R.N.; Dicke, M. Genome-wide identification, classification and expression of lipoxygenase gene family in pepper. Plant Mol. Biol. 2018, 98, 375–387. [Google Scholar] [CrossRef] [Green Version]
  14. Zhu, J.; Wang, X.; Guo, L.; Xu, Q.; Zhao, S.; Li, F.; Yan, X.; Liu, S.; Wei, C. Characterization and alternative splicing profiles of the lipoxygenase gene family in tea plant (Camellia sinensis). Plant Cell Physiol. 2018, 59, 1765–1781. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  15. Wang, J.; Hu, T.; Wang, W.; Hu, H.; Wei, Q.; Wei, X.; Bao, C. Bioinformatics analysis of the lipoxygenase gene family in radish (Raphanus sativus) and functional characterization in response to abiotic and biotic stresses. Int. J. Mol. Sci. 2019, 20, 6095. [Google Scholar] [CrossRef] [Green Version]
  16. Ogunola, O.F.; Hawkins, L.K.; Mylroie, E.; Kolomiets, M.V.; Borrego, E.; Tang, J.D.; Williams, W.P.; Warburton, M.L. Characterization of the maize lipoxygenase gene family in relation to aflatoxin accumulation resistance. PLoS ONE 2017, 12, e0181265. [Google Scholar] [CrossRef] [Green Version]
  17. Umate, P. Genome-wide analysis of lipoxygenase gene family in Arabidopsis and rice. Plant Signal. Behav. 2011, 6, 335–338. [Google Scholar] [CrossRef] [Green Version]
  18. Upadhyay, R.K.; Mattoo, A.K. Genome-wide identification of tomato (Solanum lycopersicum L.) lipoxygenases coupled with expression profiles during plant development and in response to methyl-jasmonate and wounding. J. Plant Physiol. 2018, 231, 318–328. [Google Scholar] [CrossRef]
  19. Podolyan, A.; White, J.; Jordan, B.; Winefield, C. Identification of the lipoxygenase gene family from Vitis vinifera and biochemical characterisation of two 13-lipoxygenases expressed in grape berries of Sauvignon Blanc. Funct. Plant Biol. 2010, 37, 767–784. [Google Scholar] [CrossRef]
  20. Zhang, C.; Jin, Y.; Liu, J.; Tang, Y.; Cao, S.; Qi, H. The phylogeny and expression profiles of the lipoxygenase (LOX) family genes in the melon (Cucumis melo L.) genome. Sci. Hortic. 2014, 170, 94–102. [Google Scholar] [CrossRef]
  21. Liu, S.Q.; Liu, X.H.; Jiang, L.W. Genome-wide identification, phylogeny and expression analysis of the lipoxygenase gene family in cucumber. Genet. Mol. Res. 2011, 10, 2613–2636. [Google Scholar] [CrossRef] [PubMed]
  22. Li, M.; Li, L.; Dunwell, J.M.; Qiao, X.; Liu, X.; Zhang, S. Characterization of the lipoxygenase (LOX) gene family in the Chinese white pear (Pyrus bretschneideri) and comparison with other members of the Rosaceae. BMC Genom. 2014, 15, 444. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  23. Caldelari, D.; Wang, G.; Farmer, E.E.; Dong, X. Arabidopsis lox3 lox4 double mutants are male sterile and defective in global proliferative arrest. Plant Mol. Biol. 2011, 75, 25–33. [Google Scholar] [CrossRef]
  24. Gayen, D.; Ali, N.; Sarkar, S.N.; Datta, S.K.; Datta, K. Down-regulation of lipoxygenase gene reduces degradation of carotenoids of golden rice during storage. Planta 2015, 242, 353–363. [Google Scholar] [CrossRef]
  25. Sarde, S.J.; Bouwmeester, K.; Venegas-Molina, J.; David, A.; Boland, W.; Dicke, M. Involvement of sweet pepper CaLOX2 in jasmonate-dependent induced defence against Western flower thrips. J. Integr. Plant Biol. 2019, 61, 1085–1098. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  26. Hou, Y.; Ban, Q.; Meng, K.; He, Y.; Han, S.; Jin, M.; Rao, J. Overexpression of persimmon 9-lipoxygenase DkLOX3 confers resistance to Pseudomonas syringae pv. tomato DC3000 and Botrytis cinerea in Arabidopsis. Plant Growth Regul. 2018, 84, 179–189. [Google Scholar] [CrossRef]
  27. Hou, Y.; Meng, K.; Han, Y.; Ban, Q.; Wang, B.; Suo, J.; Lv, J.; Rao, J. The persimmon 9-lipoxygenase gene DkLOX3 plays positive roles in both promoting senescence and enhancing tolerance to abiotic stress. Front Plant Sci. 2015, 6, 1073. [Google Scholar] [CrossRef] [Green Version]
  28. Chen, C.; Chen, H.; Zhang, Y.; Thomas, H.R.; Frank, M.H.; He, Y.; Xia, R. TBtools—An integrative toolkit developed for interactive analyses of big biological data. Mol. Plant 2020. [Google Scholar] [CrossRef]
  29. Zhou, Y.; Cheng, Y.; Wan, C.; Li, J.; Yang, Y.; Chen, J. Genome-wide characterization and expression analysis of the Dof gene family related to abiotic stress in watermelon. PeerJ 2020, 8, e8358. [Google Scholar] [CrossRef] [Green Version]
  30. Li, J.; Guang, Y.; Yang, Y.; Zhou, Y. Identification and expression analysis of two allene oxide cyclase (AOC) genes in watermelon. Agriculture 2019, 9, 225. [Google Scholar] [CrossRef] [Green Version]
  31. Livak, K.J.; Schmittgen, T.D. Analysis of relative gene expression data using real-time quantitative PCR and the 2−ΔΔCT method. Methods 2001, 25, 402–408. [Google Scholar] [CrossRef] [PubMed]
  32. Shaban, M.; Ahmed, M.M.; Sun, H.; Ullah, A.; Zhu, L. Genome-wide identification of lipoxygenase gene family in cotton and functional characterization in response to abiotic stresses. BMC Genom. 2018, 19, 599. [Google Scholar] [CrossRef] [PubMed]
  33. Steczko, J.; Donoho, G.P.; Clemens, J.C.; Dixon, J.E.; Axelrod, B. Conserved histidine residues in soybean lipoxygenase: Functional consequences of their replacement. Biochemistry 1992, 31, 4053–4057. [Google Scholar] [CrossRef] [PubMed]
  34. Ding, Y.; Yang, W.; Su, C.; Ma, H.; Pan, Y.; Zhang, X.; Li, J. Tandem 13-lipoxygenase genes in a cluster confers yellow-green leaf in cucumber. Int. J. Mol. Sci. 2019, 20, 3102. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  35. Sloane, D.L.; Leung, R.; Craik, C.S.; Sigal, E. A primary determinant for lipoxygenase positional specificity. Nature 1991, 354, 149–152. [Google Scholar] [CrossRef]
  36. Meng, K.; Hou, Y.; Huber, D.J.; Dong, X.; Ban, Q.; Chang, X.; Zhang, T.; Rao, J. Molecular cloning, structural characterization, and ripening-related expression of lipoxygenase genes from three persimmon cultivars differing in postharvest ripening rate. Plant Mol. Biol. Rep. 2016, 34, 854–868. [Google Scholar] [CrossRef]
  37. Li, S.T.; Zhang, M.; Fu, C.H.; Xie, S.; Zhang, Y.; Yu, L.J. Molecular cloning and characterization of two 9-lipoxygenase genes from Taxus chinensis. Plant Mol. Biol. Rep. 2012, 30, 1283–1290. [Google Scholar] [CrossRef]
  38. Padilla, M.N.; Hernández, M.L.; Sanz, C.; Martínez-Rivas, J.M. Molecular cloning, functional characterization and transcriptional regulation of a 9-lipoxygenase gene from olive. Phytochemistry 2012, 74, 58–68. [Google Scholar] [CrossRef]
  39. Hornung, E.; Walther, M.; Kühn, H.; Feussner, I. Conversion of cucumber linoleate 13-lipoxygenase to a 9-lipoxygenating species by site-directed mutagenesis. Proc. Natl. Acad. Sci. USA 1999, 96, 4192–4197. [Google Scholar] [CrossRef] [Green Version]
  40. Preston, J.; Hileman, L. Functional evolution in the plant SQUAMOSA-PROMOTER BINDING PROTEIN-LIKE (SPL) gene family. Front. Plant Sci. 2013, 4, 4. [Google Scholar] [CrossRef] [Green Version]
  41. Zhang, J. Evolution by gene duplication: An update. Trends Ecol. Evol. 2003, 18, 292–298. [Google Scholar] [CrossRef] [Green Version]
  42. Zhang, B.; Chen, K.; Bowen, J.; Allan, A.; Espley, R.; Karunairetnam, S.; Ferguson, I. Differential expression within the LOX gene family in ripening kiwifruit. J. Exp. Bot. 2006, 57, 3825–3836. [Google Scholar] [CrossRef] [Green Version]
  43. Griffiths, A.; Barry, C.; Alpuche-Solis, A.G.; Grierson, D. Ethylene and developmental signals regulate expression of lipoxygenase genes during tomato fruit ripening. J. Exp. Bot. 1999, 50, 793–798. [Google Scholar] [CrossRef]
  44. Del Ángel-Coronel, O.A.; León-García, E.; Vela-Gutiérrez, G.; Rojas-Reyes, J.O.; Gómez-Lim, M.Á.; García, H.S. Lipoxygenase activity associated to fruit ripening and senescence in chayote (Sechium edule Jacq. Sw. cv. “virens levis”). J. Food Biochem. 2018, 42, e12438. [Google Scholar] [CrossRef]
  45. Bell, E.; Creelman, R.A.; Mullet, J.E. A chloroplast lipoxygenase is required for wound-induced jasmonic acid accumulation in Arabidopsis. Proc. Natl. Acad. Sci. USA 1995, 92, 8675–8679. [Google Scholar] [CrossRef] [Green Version]
  46. Li, N.; Han, X.; Feng, D.; Yuan, D.; Huang, L.J. Signaling crosstalk between salicylic acid and ethylene/jasmonate in plant defense: Do we understand what they are whispering? Int. J. Mol. Sci. 2019, 20, 671. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  47. Di, X.; Gomila, J.; Takken, F.L.W. Involvement of salicylic acid, ethylene and jasmonic acid signalling pathways in the susceptibility of tomato to Fusarium oxysporum. Mol. Plant Pathol. 2017, 18, 1024–1035. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  48. Thaler, J.S.; Humphrey, P.T.; Whiteman, N.K. Evolution of jasmonate and salicylate signal crosstalk. Trends Plant Sci. 2012, 17, 260–270. [Google Scholar] [CrossRef] [PubMed]
  49. Wang, R.; Shen, W.; Liu, L.; Jiang, L.; Liu, Y.; Su, N.; Wan, J. A novel lipoxygenase gene from developing rice seeds confers dual position specificity and responds to wounding and insect attack. Plant Mol. Biol. 2008, 66, 401–414. [Google Scholar] [CrossRef]
  50. Liu, S.; Han, B. Differential expression pattern of an acidic 9/13-lipoxygenase in flower opening and senescence and in leaf response to phloem feeders in the tea plant. BMC Plant Biol. 2010, 10, 228. [Google Scholar] [CrossRef] [PubMed]
  51. Christensen, S.A.; Nemchenko, A.; Borrego, E.; Murray, I.; Sobhy, I.S.; Bosak, L.; DeBlasio, S.; Erb, M.; Robert, C.A.; Vaughn, K.A.; et al. The maize lipoxygenase, ZmLOX10, mediates green leaf volatile, jasmonate and herbivore-induced plant volatile production for defense against insect attack. Plant J. 2013, 74, 59–73. [Google Scholar] [CrossRef] [PubMed]
  52. He, Y.; Borrego, E.J.; Gorman, Z.; Huang, P.C.; Kolomiets, M.V. Relative contribution of LOX10, green leaf volatiles and JA to wound-induced local and systemic oxylipin and hormone signature in Zea mays (maize). Phytochemistry 2020, 174, 112334. [Google Scholar] [CrossRef] [PubMed]
  53. Gorman, Z.; Christensen, S.A.; Yan, Y.; He, Y.; Borrego, E.; Kolomiets, M.V. Green leaf volatiles and jasmonic acid enhance susceptibility to anthracnose diseases caused by Colletotrichum graminicola in maize. Mol. Plant Pathol. 2020, 21, 702–715. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  54. Upadhyay, R.K.; Handa, A.K.; Mattoo, A.K. Transcript Abundance Patterns of 9- and 13-Lipoxygenase Subfamily Gene Members in Response to Abiotic Stresses (Heat, Cold, Drought or Salt) in Tomato (Solanum lycopersicum L.) Highlights Member-Specific Dynamics Relevant to Each Stress. Genes 2019, 10, 683. [Google Scholar] [CrossRef] [Green Version]
Agriculture 10 00429 g001 550
Figure 1. Phylogenetic analysis of LOX family members in watermelon and other plant species. The NJ phylogenetic tree was created based on the full-length amino acid sequences by using MEGA 7.0 with 1000 bootstrap replicates. The information of LOX proteins in various plant species is presented in Table S2.
Figure 1. Phylogenetic analysis of LOX family members in watermelon and other plant species. The NJ phylogenetic tree was created based on the full-length amino acid sequences by using MEGA 7.0 with 1000 bootstrap replicates. The information of LOX proteins in various plant species is presented in Table S2.
Agriculture 10 00429 g001
Agriculture 10 00429 g002 550
Figure 2. Phylogenetic relationships (A), conserved domains (B) and motif compositions (C) of ClLOX proteins.
Figure 2. Phylogenetic relationships (A), conserved domains (B) and motif compositions (C) of ClLOX proteins.
Agriculture 10 00429 g002
Agriculture 10 00429 g003 550
Figure 3. Locations of the LOX genes in watermelon chromosomes.
Figure 3. Locations of the LOX genes in watermelon chromosomes.
Agriculture 10 00429 g003
Agriculture 10 00429 g004 550
Figure 4. Exon-intron arrangements of watermelon LOX genes according to phylogenetic analysis. The exons and introns are shown as blue boxes and black lines, respectively.
Figure 4. Exon-intron arrangements of watermelon LOX genes according to phylogenetic analysis. The exons and introns are shown as blue boxes and black lines, respectively.
Agriculture 10 00429 g004
Agriculture 10 00429 g005 550
Figure 5. Analysis of stress- and hormone-related cis-elements in the promoter regions (−2000 bp) of ClLOX genes. The numbers of cis-elements are boxed.
Figure 5. Analysis of stress- and hormone-related cis-elements in the promoter regions (−2000 bp) of ClLOX genes. The numbers of cis-elements are boxed.
Agriculture 10 00429 g005
Agriculture 10 00429 g006 550
Figure 6. qRT-PCR analysis of the expression of selected ClLOX genes (A–D) in different watermelon tissues. L, leaves; R, roots; S, stems; F, flowers; Fr, fruit. Error bars indicate standard deviation (SD) based on three biological replicates.
Figure 6. qRT-PCR analysis of the expression of selected ClLOX genes (A–D) in different watermelon tissues. L, leaves; R, roots; S, stems; F, flowers; Fr, fruit. Error bars indicate standard deviation (SD) based on three biological replicates.
Agriculture 10 00429 g006
Agriculture 10 00429 g007 550
Figure 7. qRT-PCR analysis of the expression of selected ClLOX genes under various hormone treatments, including JA (A,B), SA (C), and ET (D). Error bars indicate standard deviation (SD) based on three biological replicates.
Figure 7. qRT-PCR analysis of the expression of selected ClLOX genes under various hormone treatments, including JA (A,B), SA (C), and ET (D). Error bars indicate standard deviation (SD) based on three biological replicates.
Agriculture 10 00429 g007
Table
Table 1. Identification and characterization of LOX family genes in watermelon.
Table 1. Identification and characterization of LOX family genes in watermelon.
NomenclatureLocusPredicted LOX ClassChromosomal PositiongDNA (bp)CDS (bp)Protein Properties
Length (aa)MW (KDa)DomainpIGRAVYSubcellular Localization
LH2LOX
ClLOX1Cla0199089-LOXChr2: 25963474 .. 25968681 (+)5208262887599.03 40–181192–8586.14 −0.365 Cytoplasm
ClLOX2Cla0199079-LOXChr2: 25991122 .. 25996850 (+)5729264087999.70 40–181192–8625.41 −0.364 Cytoplasm
ClLOX3Cla0198979-LOXChr2: 26087261 .. 26097084 (−)9824258986297.49 18–162173–8455.67 −0.432 Cytoplasm
ClLOX4Cla0198969-LOXChr2: 26108726 .. 26117164 (−)8439225975285.95 7–9782–7355.13 −0.361 Cytoplasm
ClLOX5Cla00852013-LOXChr2: 33497808 .. 33502790 (−)49832709902102.74 74–207218–8855.76 −0.413 Chloroplast
ClLOX6Cla00851913-LOXChr2: 33513361 .. 33519238 (−)5878168656163.98 66–187342–5616.16 −0.187 Cytoplasm
ClLOX7Cla00851713-LOXChr2: 33543209 .. 33546121 (−)2913235578489.41 1–89100–7675.44 −0.447 Chloroplast
ClLOX8Cla00851613-LOXChr2: 33565766 .. 33569015 (−)3250251183695.13 3–129142–8195.72 −0.579 Chloroplast
ClLOX9Cla00321113-LOXChr2: 33577155 .. 33581164 (−)4010249383094.30 3–129140–8137.02 −0.483 Chloroplast
ClLOX10Cla00321013-LOXChr2: 33590798 .. 33596027 (−)5230198966275.43 1–6879–6456.57 −0.448 Chloroplast
ClLOX11Cla00320913-LOXChr2: 33605180 .. 33608524 (−)3345257485797.86 7–140151–8406.02 −0.558 Chloroplast
ClLOX12Cla0094029-LOXChr6: 6667738 .. 6672962 (+)52252652883100.89 36–180191–8616.00 −0.352 Cytoplasm
ClLOX13Cla00540013-LOXChr7: 27624656 .. 27628437 (+)3782175558467.73 4–128158–5846.55 −0.581 Chloroplast
ClLOX14Cla01554213-LOXChr9: 581154 .. 585338 (−)41852787928103.02 80–234245–9116.65 −0.376 Cytoplasm
ClLOX15Cla0148459-LOXChr9: 6640629 .. 6649232 (−)8604251783896.18 16–143154–8166.61 −0.459 Cytoplasm
ClLOX16Cla02298713-LOXChr11: 16214820 .. 16219598 (+)47792787928105.04 105–229240–9118.83 −0.475 Cytoplasm

Share and Cite

MDPI and ACS Style

Liu, J.; Zhou, Y.; Li, J.; Wang, F.; Yang, Y. Comprehensive Genomic Characterization and Expression Analysis of the Lipoxygenase Gene Family in Watermelon under Hormonal Treatments. Agriculture 2020, 10, 429. https://doi.org/10.3390/agriculture10100429

AMA Style

Liu J, Zhou Y, Li J, Wang F, Yang Y. Comprehensive Genomic Characterization and Expression Analysis of the Lipoxygenase Gene Family in Watermelon under Hormonal Treatments. Agriculture. 2020; 10(10):429. https://doi.org/10.3390/agriculture10100429

Chicago/Turabian Style

Liu, Jianping, Yong Zhou, Jingwen Li, Feng Wang, and Youxin Yang. 2020. "Comprehensive Genomic Characterization and Expression Analysis of the Lipoxygenase Gene Family in Watermelon under Hormonal Treatments" Agriculture 10, no. 10: 429. https://doi.org/10.3390/agriculture10100429

APA Style

Liu, J., Zhou, Y., Li, J., Wang, F., & Yang, Y. (2020). Comprehensive Genomic Characterization and Expression Analysis of the Lipoxygenase Gene Family in Watermelon under Hormonal Treatments. Agriculture, 10(10), 429. https://doi.org/10.3390/agriculture10100429

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop