NOVEL ROD-SHAPED VIRUSES ISOLATED FROM GARLIC, ALLIUM-SATIVUM, POSSESSING A UNIQUE GENOME ORGANIZATION

Rod-shaped flexuous viruses were partially purified from garlic plants (Allium sativum) showing typical mosaic symptoms. The genome was show n to be composed of RNA with a poly(A) tail of an estimated size of 10 kb as shown by denaturing agarose gel electrophoresis. We constructed cDNA libraries and screened four independent clones, which were desig nated GV-A, GV-B, GV-C and GV-D, using Northern and Southern blot hybr idization. Nucleotide sequence determination of the cDNAs, two of whic h correspond to nearly one-third of the virus genomic RNA, shows that all of these viruses possess an identical genomic structure and that a lso at least four proteins are encoded in the viral cDNA, their M(r)s being estimated to be 15K, 27K, 40K and 11K. The 15K open reading fram e (ORF) encodes the core-like sequence of a zinc finger protein preced ed by a cluster of basic amino acid residues. The 27K ORF probably enc odes the viral coat protein (CP), based on both the existence of some conserved sequences observed in many other rod-shaped or flexuous viru s CPs and an overall amino acid sequence similarity to potexvirus and carlavirus CPs. The 11K ORF shows significant amino acid sequence simi larities to the corresponding 12K proteins of the potexviruses and car laviruses. On the other hand, the 40K ORF product does not resemble an y other plant virus gene products reported so far. The genomic organiz ation in the 3' region of the garlic viruses resembles, but clearly di ffers from, that of carlaviruses. Phylogenetic analysis based upon the amino acid sequence of the viral capsid protein also indicates that t he garlic viruses have a unique and distinct domain different from tho se of the potexvirus and carlavirus groups. The results suggest that t he garlic viruses described here belong to an unclassified and new vir us group closely related to the carlaviruses.