Interaction of the Carlavirus Cysteine-Rich Protein with the Plant Defense System

Abstract

The genome of viruses of the genus Carlavirus codes for a small cysteine-rich protein (CRP) with unknown functions. To study the role of CRP of the chrysanthemum virus B (CVB), a recombinant potato virus X (PVX) genome containing the CVB CRP gene was constructed. Expression of CVB CRP in the PVX genetic surrounding drastically changed the character of symptoms produced by PVX in Nicotiana benthamiana. The recombinant virus caused local necrotic lesions of inoculated leaves and necrosis of apical leaves rather than asymptomatic infection and mild mosaic, which are caused by PVX in this host plant. In N. tabacum, the infection pattern depended on the plant host genotype: recombinant PVX spread systemically only in plants carrying the N gene. Agroinfiltration-mediated transient expression assays showed that CRP neither acts as an avirulence factor in N. benthamiana nor suppresses posttranscriptional gene silencing. CVB CRP was identified as a virus pathogenicity determinant that controls the interaction of the virus with the host plant in a way that depends on plant defense, which is mediated by resistance genes such as the N gene.