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 i nteraction (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 res istance genes Nx, Nb, and Rx. Substitution of the Thr 122 on the CP wi th a Lys in PVX strain HE has been shown to affect the response of pot ato cultivars with the Rx resistance gene. In PVX DX the avirulence de terminant 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 g enes. Sequencing of the CP gene of PVX MS (EMBL accession number Z3426 1) shows that it has a Thr in codon 122 and a Gin in codon 78. These r esults suggest that, in addition to the coat protein gene, other regio ns of the viral genome are involved in the pathogenicity.