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The complete nucleotide sequence of Rice necrosis mosaic virus (RNMV) RNA1 was determined to be 7178 nt long with one large open reading frame, potentially encoding a polyprotein of 258 kDa with the features of a typical bymovirus. The nucleotide sequence showed 56 % identity with that of Barley mild mosaic virus (BaMMV) and 46 % with those of Oat mosaic virus, Barley yellow mosaic virus and Wheat yellow mosaic virus. RNA2 was 3579 nt long, encoding a 110-kDa polyprotein, and showed 42 and 35/26 % identity with BaMMV and others, respectively. Phylogenetic analysis showed that bymoviruses were classified into two subgroups. [ABSTRACT FROM AUTHOR]

Cucumber green mottle mosaic virus (CGMMV), a member of the genus Tobamovirus, is a major threat to economically important cucurbit crops worldwide. An attenuated strain (SH33b) derived from a severe strain (SH) of CGMMV caused a reduction in the viral RNA accumulation and the attenuation of symptoms, and it has been successfully used to protect muskmelon plants against severe strains in Japan. In this study, we compared GFP-induced silencing suppression by the 129K protein and the methyltransferase domain plus intervening region (MTIR) of the 129K protein between the SH and SH33b strains, respectively. As a result, silencing suppression activity (SSA) in the GFP-silenced plants was inhibited efficiently by the MTIR and 129K protein of SH strain, and it coincided with drastically reduced accumulation of GFP-specific small interfering RNAs (siRNAs) but not by that of SH33b strain. Furthermore, analyses of siRNA binding capability (SBC) by the MTIR of 129K protein and 129K protein using electrophoretic mobility shift assay revealed that SBC was found with the MTIR and 129K protein of SH but not with that of SH33b, suggesting that a single amino acid mutation (E to G) in the MTIR is responsible for impaired SSA and SBC of SH33b. These data suggest that a single amino acid substitution in the intervening region of 129K protein of CGMMV resulted in attenuated symptoms by affecting RNA silencing suppression. [ABSTRACT FROM AUTHOR]

RNA-dependent RNA polymerases (RDRs) play key roles in gene silencing. The rice RDR6 gene was analyzed in response to viral, bacterial and fungal pathogens, after inoculation of a rice mutant line of OsRDR6, shl2- rol, with Cucumber mosaic virus, Rice necrosis mosaic virus, Xanthomonas oryzae pv. oryzae or Magnaporthe oryzae. Compared with the wild type, the mutant line accumulated more viral RNA after inoculation with the viruses and developed more severe symptoms after inoculation with the bacterium or fungus. Thus, the OsRDR6-mediated RNA silencing pathway seems to participate in defense against not only viruses, but also bacterial and fungal pathogens. [ABSTRACT FROM AUTHOR]