title: 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.
abstract: 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.
authors.affiliation: Pathogen Plant Interactions Group, Plant Breeding Science, Graduate School of Agriculture, Hokkaido University, Sapporo, Japan.
authors.forename: M L M
authors.initials: ML
authors.lastname: Yambao
authors.forename: H
authors.initials: H
authors.lastname: Yagihashi
authors.forename: H
authors.initials: H
authors.lastname: Sekiguchi
authors.forename: T
authors.initials: T
authors.lastname: Sekiguchi
authors.forename: T
authors.initials: T
authors.lastname: Sasaki
authors.forename: M
authors.initials: M
authors.lastname: Sato
authors.forename: G
authors.initials: G
authors.lastname: Atsumi
authors.forename: Y
authors.initials: Y
authors.lastname: Tacahashi
authors.forename: K S
authors.initials: KS
authors.lastname: Nakahara
authors.forename: I
authors.initials: I
authors.lastname: Uyeda
mesh_terms: 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
chemical_list: 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