Point mutations in helper component protease of clover yellow vein virus are associated with the attenuation of RNA-silencing suppression activity and symptom expression in broad bean.
Helper component protease (HC-Pro) is a potyvirus-encoded multifunctional protein and a major determinant of symptom expression in a susceptible plant. Here, we show the involvement of clover yellow vein virus (ClYVV) HC-Pro in necrotic symptom expression in broad bean (Vicia faba cv. Wase). In this host, lethal necrosis was induced by ClYVV no. 30, from which a spontaneous, mosaic-inducing mutant (MM) was obtained. Mapping with chimeric viruses between ClYVV no. 30 and MM attributed the symptom attenuation to two mutations at the HC-Pro positions 27 (threonine to isoleucine) and 193 (aspartic acid to tyrosine). Although neither mutant with the single amino acid substitution at position 27 or 193 (ClYVV/T27I or D193Y) induced the lethal necrosis, ClYVV/T27I still retained the ability to induce necrotic symptoms, but ClYVV/D193Y scarcely did so. The virus accumulation of ClYVV/D193Y was also lower than that of ClYVV no. 30. The mutations, T27I and D193Y, are located in a putative zinc finger domain and in one (N-terminal) of the two RNA binding domains, respectively, of HC-Pro. RNA-silencing suppression (RSS) activity of P1/HC-Pro in Nicotiana benthamiana was weakened by both mutations. Our results suggest a correlation between viral virulence and RSS function and the importance of the two domains in HC-Pro.
Yambao
M L M
ML
Pathogen Plant Interactions Group, Plant Breeding Science, Graduate School of Agriculture, Hokkaido University, Sapporo, Japan.
Yagihashi
H
H
Sekiguchi
H
H
Sekiguchi
T
T
Sasaki
T
T
Sato
M
M
Atsumi
G
G
Tacahashi
Y
Y
Nakahara
K S
KS
Uyeda
I
I
D002352:Carrier Proteins; D003546:Cysteine Endopeptidases / Q000737:chemistry / Q000235:genetics* / Q000494:pharmacology / Q000502:physiology; D010935:Plant Diseases / Q000209:etiology / Q000821:virology; D017354:Point Mutation; D017800:Potyvirus / Q000235:genetics* / Q000502:physiology*; D034622:RNA Interference / Q000187:drug effects / Q000502:physiology*; D013489:Suppression, Genetic / Q000187:drug effects / Q000502:physiology; D014026:Nicotiana / Q000821:virology; D025521:Tumor Suppressor Proteins; D031307:Vicia faba / Q000821:virology*; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism / Q000494:pharmacology / Q000502:physiology; D018832:Molecular Chaperones
D002352:Carrier Proteins; D003546:Cysteine Endopeptidases; D025521:Tumor Suppressor Proteins; D014764:Viral Proteins; C101119:ST13 protein, human; D018832:Molecular Chaperones; C072775:HC-Pro protein, potyvirus