[RNA silencing, the fundamental security strategy of genomic immunity: a review].

The 21-24 nucleotides small RNA that generated from double strands RNA can trigger two types of epigenetic gene silencing in plants. One is Post-Transcriptional Gene Silencing (PTGS), characterized by cleavage of homologous mRNA in cytoplasm. Transcriptional Gene Silencing (TGS) is another one, in which transcription inhibition is obtained through small RNA-directed DNA methylation of homologous promoter region. Here we summarized the relationship and differences between PTGS and TGS, the current achievement in the study of RNA silencing spreading, as well as the discrepancy of exogenous and endogenous gene silencing, and discussed the underlying reasons in the end.