Post-transcriptional gene silencing in plants: a double-edged sword

In plants, post-transcriptional gene silencing (PTGS) protects the genome from foreign genes and restricts the expression of certain endogenous genes for proper development. Here, we review the recent progress about how the unwanted PTGS is avoided in plants. As a decision-making step of PTGS, aberrant transcripts from most endogenous coding genes are strictly sorted to the bidirectional RNA decay pathways in cytoplasm but not to the short interference RNA (siRNA)-mediated PTGS, with the exception of a few development-relevant endogenous siRNA-producing genes. We also discuss a finely balanced PTGS threshold model that plants fully take advantage of the power of PTGS without self-harm.