Analyses of molecular mechanism of yellow symptoms induced by Cucumber mosaic virus Y satellite RNA

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Cucumber mosaic virus (CMV) Y satellite RNA (Y-sat) specifically induces a bright yellow mosaic on tobacco through RNA silencing machinery. In this study, I investigated the roles of major RNA silencing components such as DCLs and RDR6 in the Y-sat-mediated yellow induction. By using a virus-induced gene silencing strategy against DCLs and RDR, I found that the accumulation levels of CMV RNAs, Y-sat, DCL2, DCL4 and RDR6 mRNAs changed in a complicated manner interfering with each other. Based on transcript analyses, it was found that DCL4 was more important than DCL2 in affecting the accumulation levels of CMV and Y-sat and thus to generate 21-nt siRNAs of Y-sat. It was also found that Y-sat siRNA levels were positively correlated with the degree of yellowing. In addition, the yellow induction by Y-sat was apparently independent of RDR6, but RDR6 indirectly affects the yellow symptoms because decreased levels of RDR6 enhanced Y-sat siRNA levels and eventually enhanced yellowing.