RESUMO
ABSTRACT The Capsicum spp. L genes (L(1) to L(4)) confer resistance to tobamoviruses. Currently, the L(4) gene from Capsicum chacoense is the most effective resistance gene and has been used widely in breeding programs in Japan which have developed new resistant cultivars against Pepper mild mottle virus (PMMoV). However, in 2004, mild mosaic symptoms began appearing on the leaves of commercial pepper plants in the field which possessed the L(4) resistance gene. Serological and biological assays on Capsicum spp. identified the causal virus strain as a previously unreported pathotype, P(1,2,3,4). PMMoV sequence analysis of the virus and site-directed mutagenesis using a PMMoV-J of the P(1,2) pathotype revealed that two amino acid substitutions in the coat protein, Gln to Arg at position 46 and Gly to Lys at position 85, were responsible for overcoming the L(4) resistance gene.
RESUMO
The genome of Cucumber yellows virus (CuYV), isolated in Japan from cucumber (Cucumis sativus L.), was completely sequenced and shown to be bipartite. CuYV RNA1 consisted of 7889 nucleotides and encompassed seven open reading frames (ORFs), which is typical of the Closteroviridae, including a heat-shock protein 70 homologue, a coat protein and a diverged coat protein (CPd). CuYV RNA2 consisted of 7607 nucleotides and included two ORFs: ORF1a potentially encoded a polyprotein containing putative papain-like protease, methyltransferase and helicase domains, and ORF 1b potentially encoded an RNA-dependent RNA polymerase, which is probably expressed via a +1 ribosomal frameshift. The size and organization of the CuYV genome are similar to those of Lettuce infectious yellows virus (LIYV), the type member of the genus Crinivirus in the family Closteroviridae, indicating that CuYV is a member of that genus, although CuYV differed in several points from LIYV.
