COAT PROTEIN-SEQUENCE OF A RESISTANCE-BREAKING STRAIN OF POTATO-VIRUS-X ISOLATED IN ARGENTINA

The PVX coat protein (CP) is involved in many aspects of plant-virus interaction (virion morphology, plant symptoms, viral pathogenesis and virulence, and genomic RNA accumulation). Different virus strains have been distinguished according to their compatibility with the host resistance genes Nx, Nb, and Rx. Substitution of the Thr 122 on the CP with a Lys in PVX strain HE has been shown to affect the response of potato cultivars with the Rx resistance gene. In PVX DX the avirulence determinant for the Nx gene has been localized in the Gin 78 of the coat. PVX strain MS, like PVX HE, is able to overcome the Rx, Nx, and Nb genes. Sequencing of the CP gene of PVX MS (EMBL accession number Z34261) shows that it has a Thr in codon 122 and a Gin in codon 78. These results suggest that, in addition to the coat protein gene, other regions of the viral genome are involved in the pathogenicity.