1997 Volume 63 Issue 4 Pages 289-297
The leguminous strain of cucumber mosaic virus (CMV-L) systemically infects cowpea (Vigna unguiculata (L.) Walp.), whereas many other strains of CMV induce necrotic local lesions on inoculated leaves and do not spread systemically. The cDNAs of genomic RNAs of CMV-L were synthesized and nucleotide sequences were determined. RNA 1 was 3359 nucleotides (nt) long, and had one large open reading frame (ORF) that coded for a protein of Mr 111, 491, the la protein. RNA 2 consisted of 3047 nt and was able to encode the 2a protein of Mr 96, 720. RNA 3 was composed of 2213 nt and had two cistrons for the 3a protein and coat protein (CP). The 3a protein was encoded in the 5' proximal ORF and predicted to be a protein of Mr 30, 478. The CP gene was on the 3' proximal and coded for a protein of Mr 24, 191. Similarities in the nucleotide and amino acid sequences of RNAs 1 to 3 between CMV-L and Y strain of CMV (CMV-Y) were above 94%. In particular, the 3a protein of CMV-L showed no sequence divergence from that of CMV-Y. The infectious in vitro transcripts derived from full-length cDNA clones of CMV-Y and-L were reassorted between two viruses and used to inoculate cowpea. RNA 2 was solely necessary for the determination of infection types on cowpea, whereas RNA 3 of CMV-Y could modify the symptoms. Alignment analysis of the 2a proteins of several strains of CMV, including MB-8 that infects cowpea systemically, revealed several specific amino acid changes found in the leguminous strains or isolates.
