mRNA decay in plants: both quantity and quality matter.

In eukaryotes, degradation of messenger RNAs (mRNAs) is required for both mRNA quantity and quality control. Fine-tuning of the abundance of mRNAs that are to be translated can be achieved through a deadenylation-mediated RNA decay pathway involving progressive removal of poly(A) tails, decapping and exoribonuclease digestion. While the classical view assumes that mRNAs are degraded only after their exit from protein translation, recent studies have revealed mRNA decay can occur during translation in plants. Those mRNAs that have structural or functional defects can be filtered by translation-dependent RNA quality control pathways and rapidly degraded, so that translation fidelity is preserved. In addition, aberrant transcripts can also be efficiently eliminated through bidirectional RNA decay pathways. In the absence of those pathways, accumulation of those aberrant transcripts evokes the activation of RNA silencing, with detrimental consequences.