Search Results (9)

Citrus yellow vein clearing virus (CYVCV) is the causative agent of the yellow vein clearing disease (YVCD), a worldwide and highly destructive disease in lemon (Citrus lemon) and sour orange trees (C. aurantium). The typical symptoms of vein clearing are believed to be associated with CYVCV infection in citrus, so virus-specific diagnostic systems are currently used to confirm infection. In the present study, virome analysis based on high-throughput sequencing (HTS) on a lemon plant showing YVCD revealed mixed infection of CYVCV, iris domestica betaflexyviridae 1 (IDBV), and hop stunt viroid (HSVd). This multiple infection was confirmed in other two lemon plants with similar symptoms using virus/viroid specific primers. This is the first report of IDBV in lemon. Through molecular characterization and the reconstruction of phylogenetic relationships, a possible origin of the viruses/viroid identified in lemon has been hypothesized. Such mixed infections raise new questions about their role in the expression of YVCD symptoms observed on lemon. Full article

Plant viruses have been known to alter host metabolites that influence the attraction of insect vectors. Our study investigated whether Citrus yellow vein clearing virus (CYVCV) infection influences vector attractiveness, focusing on the citrus whitefly, Dialeurodes citri (Ashmead). Free choice assays showed that citrus whiteflies exhibited a preference for settling on CYVCV-infected lemon plants versus healthy control plants. Using chromatography techniques, we found that the levels of sugars were similar in leaves and stems of both plant groups, while the contents of several amino acids in leaf or stem samples and non-volatile phenolic compounds in the leaf samples of CYVCV-infected and healthy plants differ drastically. In addition, volatile terpenes/terpenoids decreased significantly in virus-infected plants compared to healthy controls. Several of the identified volatile compounds such as α-phellandrene, α-terpinolene, p-cymene, linalool, and citral are known for their whitefly repellent properties. Further Y-tube olfactometer bioassays revealed that emissions of volatile organic compounds (VOCs) from infected plants attracted more citrus whiteflies, but not alate spirea aphids, Aphis spiraecola Patch, than those from healthy plants, suggesting that the VOCs released from CYVCV-infected lemon plants may specifically affect citrus whiteflies. Therefore, we suggest that, in addition to the visual cue of yellow vein symptoms, the preference of citrus whiteflies that settled on CYVCV-infected lemon plants was attributed to a reduction in the levels of repellent volatile compounds. Full article

The citrus yellow vein clearing virus (CYVCV) is an emerging threat to the U.S. citrus industry. Reports from China shows it cause significant reductions in fruit yield and growth, particularly in lemon trees. In 2022, CYVCV was detected in a wide range of citrus cultivars in localized urban properties in Tulare, California. In 2024, a CYVCV-infected lemon tree was detected in Hacienda Heights in Los Angeles County, California, geographically separated from the Tulare foci. Through long-read sequencing technology, the whole-genome sequence of a CYVCV isolate from Hacienda Heights (designated as CYVCV-CA-HH1, Accession number PP840891.1) was obtained. Sequence alignments and neighbornet analysis strongly suggested that the CYVCV-CA-HH1 isolate has a different origin than the Tulare CYVCV (CYVCV CA-TL) isolates. The CYVCV CA-TL isolates were grouped with those from South Asia (India and Pakistan) and the Middle East (Türkiye), while the CYVCV-CA-HH1 isolate was grouped with isolates from East Asia (China and South Korea). Maximum likelihood phylogenetic analysis further supports this finding, showing that the CYVCV-CA-HH1 isolate shares the most recent common ancestor with a South Korean lineage, which derives from Chinese isolates. Together, our data suggest a diverse geological origin of CYVCV isolates in California. Full article

The citrus whitefly, Dialeurodes citri, is a destructive pest that infests citrus plants. It is a major vector in transmitting plant viruses such as citrus yellow vein clearing virus (CYVCV), which has caused severe economic losses worldwide, and therefore efficient control of this pest is economically important. However, the scope of genetic studies primarily focused on D. citri is restricted, something that has potentially limited further study of efficient control options. To explore the functionalities of D. citri target genes, screening for specific reference genes using RT-qPCR under different experimental conditions is essential for the furtherance of biological studies concerning D. citri. The eight candidate reference genes were evaluated by dedicated algorithms (geNorm, Normfinder, BestKeeper and ΔCt method) under five specific experimental conditions (developmental stage, sex, tissue, population and temperature). In addition, the RefFinder software, a comprehensive evaluation platform integrating all of the above algorithms, ranked the expression stability of eight candidate reference genes. The results showed that the best reference genes under different experimental settings were V-ATP-A and RPS18 at different developmental stages; α-tubulin, 18S and V-ATP-A in both sexes; EF1A and α-tubulin in different tissues; Actin and Argk under different populations; and RPS18 and RPL13 in different temperatures. The validation of selected reference genes was further identified using heat shock protein (Hsp) 70 as a reporter gene. Our study, for the first time, provides a detailed compilation of internal reference genes for D. citri that are suitable for RT-qPCR analysis, which is robust groundwork for comprehensive investigation of the functional target genes of D. citri. Full article

Background: Citrus yellow vein-clearing virus (CYVCV) is a Mandarivirus that causes great economic losses in lemon production. CYVCV infection is associated with obvious yellow vein-clearing disease symptoms and is directly regulated by plant hormone responses. Methods: To understand how lemon plants respond to CYVCV infection, we performed transcriptomic and phytohormone metabolomics. Results: A total of 936 differentially expressed genes were identified, and 773 were downregulated. Salicylic acid and auxin levels increased after CYVCV infection, and phytohormone regulatory systems were also explored. Jasmonic acid and auxin levels decreased after the CYVCV challenge, and jasmonic acid and auxin signaling pathway components were mostly downregulated. The differentially expressed genes (DEGs) involved in the immune response to viral infection, including those related to cell wall integrity, lectin, microtubules, and mildew resistance locus O (MLO), may also provide new candidate targets for CYVCV control. Conclusions: Our findings provide new insights into the molecular changes underlying the pathogenesis of CYVCV in lemon plants. Full article

The Citrus yellow vein clearing virus (CYVCV) causes a viral disease that has been reported in some citrus-growing regions in countries in Eurasia including Pakistan, India, Türkiye, Iran, China, and South Korea. Recently, CYVCV was detected in a localized urban area in a town in the middle of California’s citrus-growing region and marks the first occurrence of the virus in North America. CYVCV has been reported to be spread by aphid and whitefly vectors and is graft and mechanically transmitted. Hence, it is an invasive pathogen that presents a significant threat to the California citrus industry, especially lemons, which are highly symptomatic to CYVCV. To elucidate the origin of the CYVCV California strain, we used long-read sequencing technology and obtained the complete genomes of three California CYVCV isolates, CA1, CA2, and CA3. The sequences of these isolates exhibited intergenomic similarities ranging from 95.4% to 97.4% to 54 publicly available CYVCV genome sequences, which indicated a relatively low level of heterogeneity. However, CYVCV CA isolates formed a distinct clade from the other isolates when aligned against other CYVCV genomes and coat protein gene sequences as shown by the neighbor network analysis. Based on the rooted Maximum Likelihood phylogenetic trees, CYVCV CA isolates shared the most recent common ancestor with isolates from India/South Asia. Bayesian evolutionary inferences resulted in a spatiotemporal reconstruction, suggesting that the CYVCV CA lineage diverged from the Indian lineage possibly around 1995. This analysis placed the origin of all CYVCV to around 1990, with South Asia and/or Middle East as the most plausible geographic source, which matches to the first discovery of CYVCV in Pakistan in 1988. Moreover, the spatiotemporal phylogenetic analysis indicated an additional virus diffusion pathway: one from South Asia to China and South Korea. Collectively, our phylogenetic inferences offer insights into the probable dynamics of global CYVCV dissemination, emphasizing the need for citrus industries and regulatory agencies to closely monitor citrus commodities crossing state and international borders. Full article

Citrus are affected by many viruses and viroids, some globally widespread and some restricted to particular countries or areas. In this study, we simulated the use of high throughput sequencing (HTS) and the bioinformatic analysis of small interfering RNAs (siRNA) as a pre-screening method to guide bioindexing and molecular detection to enhance the surveillance survey of some key or emerging citrus viruses, such as non-European citrus tristeza virus isolates (non-EU CTV), citrus tatter leaf virus, citrus leprosis virus, citrus yellow mosaic virus, and citrus bark cracking viroid, present in the EPPO lists, and the citrus yellow vein clearing virus. The HTS’s ability to detect other citrus viroids was also evaluated. The results demonstrate that HTS provides a comprehensive phytosanitary status of citrus samples either in single and multiple infections of viruses and viroids. It also provides effective information on citrus tristeza virus mixed infections despite not being able to identify the non-EU variants of the virus. Bioindexing checks each single virus infection but does not differentiate viroids on the Etrog citron indicator and is time-consuming. Molecular assays are valuable as confirmation tests of viruses and viroids but many pairs of primers are needed for a full screening and new or non-target pathogens remain undetected. In addition, the genomes of two isolates of the citrus yellow vein clearing virus and the citrus tatter leaf virus, detected in a sample from China, are described. Full article

Citrus yellow vein clearing virus is a newly accepted member of the genus Mandarivirus in the family Alphaflexiviridae. The triple gene block proteins (TGBp1, TGBp2 and TGBp3) encoded by plant viruses in this family function on facilitating virus movement. However, the protein function of citrus yellow vein clearing virus (CYVCV) have never been explored. Here, we showed in both yeast two-hybrid (Y2H) and bimolecular fluorescence (BiFC) assays that the coat protein (CP), TGBp1 and TGBp2 of CYVCV are self-interacting. Its CP also interacts with all three TGB proteins, and TGBp1 and TGBp2 interact with each other but not with TGBp3. Furthermore, the viral CP colocalizes with TGBp1 and TGBp3 at the plasmodesmata (PD) of epidermal cells of Nicotiana benthamiana leaves, and TGBp1 can translocate TGBp2 from granular-like structures embedded within ER networks to the PD. The results suggest that these proteins could coexist at the PD of epidermal cells of N. benthamiana. Using Agrobacterium infiltration-mediated RNA silencing assays, we show that CYVCV CP is a strong RNA silencing suppressor (RSS) triggered by positive-sense green fluorescent protein (GFP) RNA. The presented results provide insights for further revealing the mechanism of the viral movement and suppression of RNA silencing. Full article