Progress in molecular mechanism of RNA silencing in plants

RNA silencing is a defense mechanism in eukaryotes which can resist the exogenous genetic factors (virus,transposon or transgene)and regulate gene expression.It was found that many important enzymes and proteins are involved in the RNA silencing of plants,including 6 kinds of RNA-dependent RNA polymerases, 4 types of Dicer-like(DCL)endoribonucleases and 10 kinds of argonautes protein.In plants,four RNA silencing pathways are directed by microRNAs(miRNAs)and three types of small interfering RNAs(siRNAs)which are trans-acting siRNAs(ta-siRNAs),natural antiseuse siRNAs(nat-siRNAs)and heterochromatin siRNAs(hc- siRNAs).In the systematic RNA silencing,DCL4 or/and DCL2 process dsRNAs into the secondary siRNAs to amplify silencing signals and effects.