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

Ana P Luna,Laura Cerero,Araceli G Castillo,Edgar A Rodríguez-Negrete,Eduardo R Bejarano,Beatriz Romero-Rodríguez,Tábata Rosas-Díaz

doi:10.3389/fpls.2020.00835

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.

Highlights

Geminiviruses constitute a group of circular single-stranded DNA plant viruses that infect a wide range of plants and cause substantial yield losses worldwide (Rojas et al, 2018; García-Arenal and Zerbini, 2019)
In begomoviral V2, two highly conserved protein domains have been identified to be essential for its activity as post-transcriptional gene silencing (PTGS) suppressor (Supplementary Figure S1): (i) a putative CK2/protein kinase C (PKC) phosphorylation motif (Chowda-Reddy et al, 2008) and (ii) a CxC motif (Glick et al, 2008) that is required for full infection (Hak et al, 2015)
We have identified and characterized three domains of V2 from curtovirus required for PTGS suppression activity, subcellular localization and systemic, but not local infection

Summary

Introduction

Geminiviruses constitute a group of circular single-stranded DNA plant viruses that infect a wide range of plants and cause substantial yield losses worldwide (Rojas et al, 2018; García-Arenal and Zerbini, 2019). Curtoviruses are important pathogens for many cultivated and wild plant species. This genus only has three species, including the model species Beet curly top virus (BCTV), it has an enormously wide host range within dicot plants, including around 300 species in more than 40 plant families, as well as a broad geographical distribution that includes the Indian subcontinent, North and Central America and the Mediterranean region (Varsani et al, 2014). The virion sense strand contains two ORFs (V2 and V1, that encodes the coat protein, CP), and a third one (V3) which is only present in some of the nine genera, including Curtovirus but not Begomovirus. The complementary sense strand encompasses up to four ORFs (C1, C2, C3, and C4)

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