The resistance mechanism of plants against virus infection

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Okuno's group found that to suppress Red clover necrotic mosaic virus (RCNMV) needs multiple viral components, including viral RNAs and putative RNA replicase proteins. A close relationship between the RNA elements required for negative-strand RNA synthesis and RNAi suppression suggests a strong link between the viral RNA replication machinery and the RNAi machinery. DCL1 mutants of Arabidopsis thaliana did not support RCNMV infection, suggesting DCL1 is a host component required for RCNMV infection. RCNMV preferentially interferes with the accumulation of long small-interfering RNAs (24-26 nt) in RNAi induced by a hairpin dsRNA. We propose a model in which, to replicate, RCNMV deprives the RNAi machinery of a factor that is probably a dicer-like protein, and suppresses Dicer-mediated dsRNA cleavage. They also found that the stem-loop structure that functions as a trans-activator for the RNA-mediated CP expression is critically required for RNA2 replication of RCNMV itself.Watanabe's group found that DCL1 catalyzes at least the first and second cleavage steps in miRNA biogenesis and that double-stranded RNA-binding domains of DCL1 are involved in positioning of the cleavage sites. Our result is direct evidence that DCL1 is involved in processing of pri-and pre-miRNA. (dsRNA )-binding domains of DCL1 are involved in positioning of the cleavage sites. They also identified several proteins associated with Tobacco mosaic virus movement protein in plasmodesmata.