siRNA-mediated DNA methylation and H3K9 di- methylation in plants INI-REVIEW M

Heterochromatic siRNAs regulate transcriptional gene silencing by inducing DNA methylation and histone H3K9 dimethylation. Recent advances have revealed the distinct phases involved in siRNA mediated silencing pathway, although the precise functions of a number of factors remain undesignated, putative mechanisms for the con- nection between DNA and histone methylation have been investigated, and much effort has been invested to understand the biological functions of siRNA-mediated epigenetic modifi cation. In this review, we summarize the mechanism of siRNA-mediated epigenetic modification, which involves the production of siRNA and the recruit- ments of DNA and histone methytransferases to the target sequences assisted by complementary pairing between 24-nt siRNAs and nascent scaffold RNAs, the roles of siRNA- mediated epigenetic modifi cation in maintaining genome stability and regulating gene expression have been dis- cussed, newly identified players of the siRNA mediated silencing pathway have also been introduced.