Adaptation of Soybean mosaic virus avirulent chimeras containing P3 sequences from virulent strains to Rsv1-genotype soybeans is mediated by mutations in HC-Pro.
In Rsv1-genotype soybean, Soybean mosaic virus (SMV)-N (an avirulent isolate of strain G2) elicits extreme resistance (ER) whereas strain SMV-G7 provokes a lethal systemic hypersensitive response (LSHR). SMV-G7d, an experimentally evolved variant of SMV-G7, induces systemic mosaic. Thus, for Rsv1-genotype soybean, SMV-N is avirulent whereas SMV-G7 and SMV-G7d are both virulent. Exploiting these differential interactions, we recently mapped the elicitor functions of SMV provoking Rsv1-mediated ER and LSHR to the N-terminal 271 amino acids of P3 from SMV-N and SMV-G7, respectively. The phenotype of both SMV-G7 and SMV-G7d were rendered avirulent on Rsv1-genotype soybean when the part of the genome encoding the N-terminus or the entire P3 cistron was replaced with that from SMV-N; however, reciprocal exchanges did not confer virulence to SMV-N-derived P3 chimeras. Here, we describe virulent SMV-N-derived P3 chimeras containing the full-length or the N-terminal P3 from SMV-G7 or SMV-G7d, with or without additional mutations in P3, that were selected on Rsv1-genotype soybean by sequential transfers on rsv1 and Rsv1-genotype soybean. Sequence analyses of the P3 and helper-component proteinase (HC-Pro) cistrons of progeny recovered from Rsv1-genotype soybean consistently revealed the presence of mutations in HC-Pro. Interestingly, the precise mutations in HC-Pro required for the adaptation varied among the chimeras. No mutation was detected in the HC-Pro of progeny passaged continuously in rsv1-genotype soybean, suggesting that selection is a consequence of pressure imposed by Rsv1. Mutations in HC-Pro alone failed to confer virulence to SMV-N; however, reconstruction of mutations in HC-Pro of the SMV-N-derived P3 chimeras resulted in virulence. Taken together, the data suggest that HC-Pro complementation of P3 is essential for SMV virulence on Rsv1-genotype soybean.
Hajimorad
M R
MR
Department of Entomology and Plant Pathology, the University of Tennessee, Knoxville 37996, USA. mrh@utk.edu
Eggenberger
A L
AL
Hill
J H
JH
D000222:Adaptation, Physiological; D000595:Amino Acid Sequence; D001483:Base Sequence; D002678:Chimera / Q000235:genetics; D003546:Cysteine Endopeptidases / Q000235:genetics; D004279:DNA, Viral / Q000235:genetics; D017343:Genes, Plant; D005814:Genes, Viral; D054884:Host-Pathogen Interactions / Q000235:genetics* / Q000502:physiology; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010935:Plant Diseases / Q000235:genetics / Q000821:virology; D017800:Potyvirus / Q000235:genetics* / Q000472:pathogenicity* / Q000502:physiology; D013025:Glycine max / Q000235:genetics* / Q000821:virology*; D014764:Viral Proteins / Q000235:genetics; D014774:Virulence / Q000235:genetics
D004279:DNA, Viral; D014764:Viral Proteins; D003546:Cysteine Endopeptidases; C072775:HC-Pro protein, potyvirus