The barley stripe mosaic virus gamma b gene encodes a multifunctional cysteine-rich protein that affects pathogenesis.
Barley stripe mosaic virus contains seven genes, one of which specifies a 17-kD cysteine-rich protein, gamma b, that is known to affect virulence. To further characterize the role of gamma b in pathogenesis, we mutagenized sequences encoding amino acids within two clusters of cysteine and histidine residues in the cysteine-rich domain and a group of basic amino acids located between the clusters and determined the effects of these mutations on the symptom phenotype in barley. Three single amino acid substitutions in cluster 1 and two amino acid exchanges in the basic region caused bleached symptoms associated with pronounced elevations in accumulation of gamma b protein. In contrast, three single amino acid substitutions in cluster 2 and a mutation in the basic motif resulted in attenuated ("null") symptoms typical of those produced when the gamma b gene is deleted. Tissue infected with these "null" mutants accumulated slightly elevated amounts of the gamma b protein but significantly lower levels of coat protein and the putative movement protein beta b. Genetic complementation tests revealed that cluster 1 mutations are dominant over the wild-type gamma b gene, whereas those in cluster 2 are recessive. These results highlight the pivotal role of gamma b in pathogenesis and suggest that the two cysteine-rich clusters are functionally distinct and that they affect different aspects of disease development.
Donald
R G
RG
Department of Plant Biology, University of California, Berkeley 94720.
Jackson
A O
AO
D000595:Amino Acid Sequence; D001483:Base Sequence; D002451:Cell Compartmentation; D003001:Cloning, Molecular; D003545:Cysteine; D003593:Cytoplasm / Q000821:virology; D005814:Genes, Viral / Q000235:genetics*; D001467:Hordeum / Q000821:virology*; D008969:Molecular Sequence Data; D009029:Mosaic Viruses / Q000235:genetics* / Q000472:pathogenicity; D009154:Mutation; D010641:Phenotype; D010935:Plant Diseases / Q000209:etiology; D017421:Sequence Analysis; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic; D017361:Viral Nonstructural Proteins / Q000096:biosynthesis*; D014764:Viral Proteins / Q000096:biosynthesis; D014777:Virus Diseases / Q000209:etiology
D017361:Viral Nonstructural Proteins; D014764:Viral Proteins; C091602:gamma(b) protein, Barley stripe mosaic virus; D003545:Cysteine