Open AccessOne Amino Acid Change in Cucumber Mosaic Virus RNA Polymerase Determines Virulent/Avirulent Phenotypes on Cowpea
Author(s) -
Akira Karasawa,
Itaru Okada,
Kayoko Akashi,
Yutaka Chida,
S. Hase,
Yoshiko Nakazawa-Nasu,
Akiko Ito,
Yoshio Ehara
Publication year - 1999
Publication title -
phytopathology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.264
H-Index - 131
eISSN - 1943-7684
pISSN - 0031-949X
DOI - 10.1094/phyto.1999.89.12.1186
Subject(s) - biology , cucumber mosaic virus , rna dependent rna polymerase , rna , gene , virulence , vigna , mutant , rna polymerase , genetics , virology , cucumovirus , complementary dna , virus , botany
The elicitation of the hypersensitive response (HR) is known to depend on the interaction between a resistance gene of a host plant and a corresponding avirulence gene of a pathogen. The cv. Kurodane-Sanjaku of cowpea (Vigna unguiculata) has the Cry locus that confers resistance against cucumber mosaic virus strain Y (CMV-Y). The resistance is overcome by infection with a legume strain of CMV (CMV-L). RNA 2, which codes for the 2a protein, a subunit of the viral replicase components, has been known to control virulent/avirulent phenotypes. We generated chimeric constructs of full-length cDNA clones of RNA 2 of both strains and inoculated infectious transcripts to delimit the domain controlling symptoms. A 243-base pair fragment containing a coding region for the GDD RNA-dependent RNA polymerase core sequence was shown to be responsible for the phenotypic differences. From sequence alignment analysis, two amino acids (Phe631 and Ala641) of the HR-type 2a protein encoded in this fragment were specifically exchanged to Tyr and Ser, respectively, in the 2a proteins of resistance-breaking strains. Point mutations introduced into RNA 2 backgrounds of both strains that were designed to change the amino acid at position 631 resulted in a change of symptoms, indicating that a single nucleotide change determines the reactions elicited by both strains. Analysis for one additional mutant RNA 2 showed that symptom determination may be correlated with the nature of the lateral chain of amino acid 631.