Characterization of Curtovirus V2 Protein, a Functional Homolog of Begomovirus V2

Abstract

Geminiviruses are single-stranded DNA plant viruses with circular genomes packaged within geminate particles. Among the Geminiviridae family, Begomovirus and Curtovirus comprise the two best characterized genera. Curtovirus and Old World begomovirus possess similar genome structures with six to seven open-reading frames (ORF). Among them, begomovirus and curtovirus V2 ORFs share the same location in the viral genome, encode proteins of similar size, but show extremely poor sequence homology between the genera. V2 from Beet curly top virus (BCTV), the model species for the Curtovirus genus, as it begomoviral counterpart, suppresses post-transcriptional gene silencing (PTGS) by impairing the RDR6/SGS3 pathway and localizes in the nucleus spanning from the perinuclear region to the cell periphery. By aminoacid sequence comparison we have identified that curtoviral and begomoviral V2 proteins shared two hydrophobic domains and a putative phosphorylation motif. These three domains are essential for BCTV V2 silencing suppression activity, for the proper nuclear localization of the protein and for systemic infection. The lack of suppression activity in the mutated versions of V2 is complemented by the impaired function of RDR6 in Nicotiana benthamiana but the ability of the viral mutants to produce a systemic infection is not recovered in gene silencing mutant backgrounds. We have also demonstrated that, as its begomoviral homolog, V2 from BCTV is able to induce systemic symptoms and necrosis associated with a hypersensitive response-like (HR-like) when expressed from Potato virus X vector in N. benthamiana, and that this pathogenicity activity does not dependent of its ability to supress PTGS.

Identification and Functional Analysis of Four RNA Silencing Suppressors in Begomovirus Croton Yellow Vein Mosaic Virus

“…V2 is considered as the strongest PTGS suppressor encoded by begomoviruses (Luna et al, 2017). It may suppress PTGS by impairing the RDR6/SGS3 pathway (Luna et al, 2020). Although previous reports and our work all showed that the expression of V2 itself is sufficient to induce pathogenicity symptoms on host plants, this activity is independent of PTGS suppression function of V2 (Luna et al, 2020).…”

The C5 protein encoded by Ageratum leaf curl Sichuan virus is a virulence factor and contributes to the virus infection

“…For example, the V2 protein of beet curly top virus (BCTV) can induce severe systemic necrosis in N. benthamiana plants, the C1 protein of apple geminivirus (AGV) can induce severe plant dwarfing symptoms, and the C4 protein of Malvastrum yellow vein virus (MaYVV) can induce N. benthamiana leaf upward rolling symptoms (Jing et al, 2019;Luna et al, 2020;Zhan et al, 2018). It is noteworthy that the AC5/C5 proteins of begomoviruses have different functions in virus infections.…”

Geminiviral Triggers and Suppressors of Plant Antiviral Immunity

“…AV2 and V2 also suppress antiviral RNA silencing in the amplification phase and interfere with host methylation activities, downstream events of TGS [77][78][79]. TYLCV V2 interacts with and inhibits the suppressor of gene silencing 3 (SGS3), the cofactor of RDR6; thereby, affecting vsiRNA amplification [80].…”

“…V2 may also sequester the RDR6/SGS3 intermediate/substrate dsRNA with 5' overhang ends from SGS3 association, further interfering with vsiRNA amplification [77,80]. Likewise, V2 from the curtovirus beet curly top virus (BCTV) has been recently shown to suppress post-transcriptional gene silencing (PTGS) by impairing the RDR6/SGS3 pathway [77,78]. CLCuMV V2 interacts with long dsRNA to prevent DCL processing, whereas tomato yellow leaf curl China virus (TYLCCV) V2 interacts with siRNAs to prevent AGO incorporation [70,81].…”