Heterologous expression of viral suppressors of RNA silencing complements virulence of the HC-Pro mutant of clover yellow vein virus in pea
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Many plant viruses encode suppressors of RNA silencing, including the helper component-proteinase (HC-Pro) of potyviruses. Our previous studies showed that a D-to-Y mutation at amino acid position 193 in HC-Pro (HC-Pro-D193Y) drastically attenuated the virulence of clover yellow vein virus (ClYVV) in legume plants. Furthermore, RNA-silencing suppression (RSS) activity of HC-Pro-D193Y was significantly reduced in Nicotiana benthamiana. Here, we examine the effect of expression of heterologous suppressors of RNA silencing, i.e., tomato bushy stunt virus p19, cucumber mosaic virus 2b, and their mutants, on the virulence of the ClYVV point mutant with D193Y (Cl-D193Y) in pea. P19 and 2b fully and partially complemented Cl-D193Y multiplication and virulence, including lethal systemic HR in pea, respectively, but the P19 and 2b mutants with defects in their RSS activity did not. Our findings strongly suggest that the D193Y mutation exclusively affects RSS activity of HC-Pro and that RSS activity is necessary for ClYVV multiplication and virulence in pea.
KeywordsCucumber Mosaic Virus Tomato Bushy Stunt Virus D193Y Mutation Clover Yellow Vein Virus White Clover Mosaic Virus
We are grateful to T. Okuno (Kyoto University) for providing the pBIC-P19. We also thank K. Goto (Hokkaido University) for helpful discussions. This study was supported in part by Grants-in-Aid for Scientific Research (S) and Young Scientists (A) from the Ministry of Science, Education, Culture, and Technology of Japan.
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