The divergent V2 protein encoded by parsley yellow leaf curl virus is a suppressor of transcriptional and post-transcriptional gene silencing and a potential symptom determinant
It is demonstrated that the divergent V2 protein from PYLCV has the capacity to function as a viral suppressor of RNA silencing (VSR) and as a potential symptom determinant, suggesting relevant roles in viral pathogenicity analogous to those of other geminiviral V2 proteins.
Abstract
The Geminiviridae family encompasses over 500 species of economically important plant viruses. A new geminivirus species named parsley yellow leaf curl virus (PYLCV) was first identified in 2020 in Southeastern Iran. The PYLCV genome, comprising 2,779 nucleotides, exhibits a pairwise sequence identity of less than 66% with other geminiviruses and encodes a divergent V2 protein that lacks sequence similarity to known proteins in GenBank. This study explores the functions of this V2 through various analyses. An assessment of the V2 amino acid composition indicates a higher prevalence of acidic residues. By expressing N-terminal and C-terminal GFP fusions (GFP-V2 and V2-GFP) in Nicotiana benthamiana, we demonstrate that V2 localizes to the cytoplasm, nucleus, endoplasmic reticulum, and the Cajal body. Notably, PYLCV V2 suppressed local PTGS and delayed systemic PTGS in GFP-based silencing assays and restored GFP transcript accumulation in a systemic 16c-TGS assay, indicating suppression of transcriptional silencing. Co-immunoprecipitation assays further showed that PYLCV V2 interacts with NbAGO4-1 and with itself, but not detectably with NbSGS3 or NbHDA6, supporting a potential role for PYLCV V2 in targeting the AGO4-mediated transcriptional silencing pathway. Ectopic expression of V2 via a PVX vector induced necrotic lesions with HR-like features, together with systemic mosaic patterns and severe leaf curling in upper leaves. Importantly, PYLCV V2 retains core V2-like biological activities despite extensive primary-sequence divergence, suggesting that functional conservation may rely on structural or biophysical determinants rather than linear sequence similarity. Our findings demonstrate that the divergent V2 protein from PYLCV has the capacity to function as a viral suppressor of RNA silencing (VSR) and as a potential symptom determinant, suggesting relevant roles in viral pathogenicity analogous to those of other geminiviral V2 proteins.
ABSTRACT Geminiviruses severely threaten global crop production. Tomato yellow leaf curl virus (TYLCV) encodes multifunctional effector C4, which participates in diverse biological processes and interacts with host proteins to facilitate infection. Despite extensive studies on geminiviral C4, how TYLCV C4 suppresses tomato immunity remains poorly characterized. In this study, we identified the tomato 14‐3‐3 protein SlTFT2 as a specific interaction partner of the TYLCV C4 protein. We demonstrated that SlTFT2 functions as a positive regulator of antiviral defence, as its silencing enhanced systemic viral infection, whereas its overexpression restricted infection. A critical serine residue at position 86 in C4 was essential for this interaction, and mutation of this residue (S86A or S86L) in TYLCV infectious clones significantly attenuated viral infectivity. Furthermore, C4, but not the S86A or S86L mutants, reduced the nuclear accumulation of SlTFT2. Collectively, our findings establish that the C4–SlTFT2 interaction is indispensable for TYLCV‐mediated immunosuppression. Moreover, C4 promotes successful TYLCV infection by reducing the nuclear accumulation of SlTFT2 through this interaction, revealing a novel mechanism by which the virus subverts host defence by targeting a 14‐3‐3 protein.
By combining next-generation sequencing (NGS), reverse transcription polymerase chain reaction (RT-PCR), and rapid amplification of cDNA ends (RACE) PCR, we sequenced from adult bean flower thrips (Megalurothrips usitatus) the near-complete genome of a previously undescribed virus (related to Anopheline-associated C virus), which we named “Megalurothrips usitatus associated virus 1” (MUaV1). The viral genome comprises two linear, single-stranded, positive-sense RNA segments, designated RNA1 (3658 nt) and RNA2 (2041 nt), which shared 35.75% and 23.74% nucleotide identity with Anopheline-associated C virus (YP_009011225.1) and chronic bee paralysis virus (ASM62179.1), respectively. According to phylogenetic analysis, MUaV1 shares the closest evolutionary relationship with Anopheline-associated C virus, followed by chronic bee paralysis virus. A clear predominance of 22 nt vsiRNAs, characteristic of Dicer-mediated siRNA processing in insects, was observed, demonstrating that MUaV1 is capable of infecting the bean flower thrips and activating its antiviral RNAi response. Our study provides the first characterization of this virus in the bean flower thrips, enhancing our understanding of the bean flower thrips virome.
Xi-Tong Zhu, Heng Li, Lin Lin et al.· Viruses· 0 citations
Plasmodesmata (PD) play vital roles in plant growth and defense through controlling symplastic transport of important molecules. Here we report that a conserved COBRA-like protein, COBL3, is required for PD-mediated antiviral defense (PMAD) against divergent plant RNA viruses in wheat (Triticum aestivum) and tobacco (Nicotiana benthamiana) via positively regulating callose accumulation. The wheat COBL3 protein, TaCOBL3, interacts with the 17K movement protein (MP) of barley yellow dwarf virus-GAV (BYDV-GAV). TaCOBL3 is associated with the plasma membrane and co-locates with 17K MP at PD. Genetic analysis with overexpression and knockout lines reveals that TaCOBL3 positively regulates wheat defense against BYDV-GAV through modulating callose accumulation at PD. Interestingly, TaCOBL3 interacts with the wheat homolog of PDLP5, a conserved key PD permeability regulator in higher plants. Silencing TaPDLP5 diminishes the elevated BYDV-GAV defense conferred by TaCOBL3 overexpression in wheat. Furthermore, transient expression of TaCOBL3 promotes callose accumulation and lowers PD permeability in tobacco cells, which is, however, largely compromised when tobacco PDLP5 is silenced. Notably, BYDV 17K MP weakens the interaction between TaCOBL3 and TaPDLP5 and inhibits their callose binding activities. Finally, silencing tobacco NbCOBL3 gene decreases callose content and attenuated host defense against two tobraviruses, one potexvirus, and one hordeivirus. Overall, our study reveals a previously unknown role of COBRA-like proteins in PMAD and provides insight into how a plant viral MP sabotages PMAD through perturbing COBL3-PDLP5 interaction to facilitate virus spread through PD. The conserved COBL3 gene may represent a valuable target for engineering broad-spectrum antiviral resistance in crop plants.
Jin Yang, Kai Gao, Xiaohuan Jin et al.· Plant Communications· 0 citations
Pepper plants exhibiting severe leaf curling and deformation in open fields in Iraq were investigated to characterize their associated virome using metatranscriptomic sequencing. High-throughput sequencing (HTS) revealed the presence of bell pepper alphaendornavirus (BPEV) and pepper cryptic virus 2 (PCV-2), together with fragmented sequences related to tobacco vein clearing virus (TVCV). A nearly complete genome of the Iraqi BPEV isolate (14,700 bp) and both genomic segments of PCV-2 (1,623 bp and 1,513 bp) were assembled and deposited in GenBank. Phylogenetic analysis showed that the BPEV isolate clustered closely with isolates from South Korea, Jamaica, and the Dominican Republic, whereas both PCV-2 genomic segments were most closely related to Turkish isolates, indicating high genetic conservation among geographically distant populations. In addition, transcriptome mapping revealed abundant expression of ten endogenous pararetroviral elements integrated within the pepper genome, with most transcripts corresponding to reverse transcriptase (RT-LTR) and RNase H domains. This study represents the first comprehensive metatranscriptomic characterization of the pepper virome in Iraq, documenting the first detection of BPEV and PCV-2 in the country while revealing extensive expression of endogenous viral elements. These findings expand current knowledge of pepper-associated viruses in the Middle East and demonstrate the value of metatranscriptomic sequencing for detecting both exogenous viruses and endogenous viral components.
Shurooq Zagier, O. Alisawi, W. Aljuaifari et al.· Jurnal Hama dan Penyakit Tum...· 0 citations
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