Mapping of a hypovirus p29 protease symptom determinant domain with sequence similarity to potyvirus HC-Pro protease.
Hypovirus infection of the chestnut blight fungus Cryphonectria parasitica results in a spectrum of phenotypic changes that can include alterations in colony morphology and significant reductions in pigmentation, asexual sporulation, and virulence (hypovirulence). Deletion of 88% [Phe(25) to Pro(243)] of the virus-encoded papain-like protease, p29, in the context of an infectious cDNA clone of the prototypic hypovirus CHV1-EP713 (recombinant virus Deltap29) partially relieved virus-mediated suppression of pigmentation and sporulation without altering the level of hypovirulence. We now report mapping of the p29 symptom determinant domain to a region extending from Phe(25) through Gln(73) by a gain-of-function analysis following progressive repair of the Deltap29 deletion mutant. This domain was previously shown to share sequence similarity [including conserved cysteine residues Cys(38), Cys(48), Cys(70), and Cys(72)] with the N-terminal portion of the potyvirus-encoded helper component-proteinase (HC-Pro), a multifunctional protein implicated in aphid-mediated transmission, genome amplification, polyprotein processing, long-distance movement, and suppression of posttranscriptional silencing. Substitution of a glycine residue for either Cys(38) or Cys(48) resulted in no qualitative or quantitative changes in virus-mediated symptoms. Unexpectedly, mutation of Cys(70) resulted in a very severe phenotype that included significantly reduced mycelial growth and profoundly altered colony morphology. In contrast, substitution for Cys(72) resulted in a less severe symptom phenotype approaching that observed for Deltap29. The finding that p29-mediated symptom expression is influenced by two cysteine residues that are conserved in the potyvirus-encoded HC-Pro raises the possibility that these related viral-papain-like proteases function in their respective fungal and plant hosts by impacting ancestrally related regulatory pathways.
Suzuki
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N
Center for Agricultural Biotechnology, University of Maryland Biotechnology Institute, College Park, Maryland 20742, USA.
Chen
B
B
Nuss
D L
DL
D001203:Ascomycota / Q000254:growth & development / Q000821:virology; D003545:Cysteine / Q000737:chemistry; D003546:Cysteine Endopeptidases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017353:Gene Deletion; D005814:Genes, Viral; D009754:Nuts / Q000382:microbiology; D017800:Potyvirus / Q000201:enzymology / Q000235:genetics; D017434:Protein Structure, Tertiary; D012328:RNA Viruses / Q000201:enzymology* / Q000235:genetics / Q000472:pathogenicity*; D012330:RNA, Double-Stranded / Q000032:analysis / Q000235:genetics; D014162:Transfection; D014764:Viral Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
D012330:RNA, Double-Stranded; D014764:Viral Proteins; D003546:Cysteine Endopeptidases; C072775:HC-Pro protein, potyvirus; C069855:protease p29; D003545:Cysteine