The role of microRNAs and other endogenous small RNAs in plant stress responses.

Crop yields are significantly reduced by biotic and abiotic stresses throughout the world. To reduce the damage caused by stress factors, plants have evolved sophisticated adaptive responses involving reprogramming gene expression at the transcriptional, post-transcriptional and post-translational levels. A better understanding of such processes will lead to new strategies to improve plant stress tolerance. Recently discovered endogenous small RNAs (microRNAs and small-interfering RNAs) have emerged as important players in plant stress responses. The observation that some of the small RNAs are up- or down-regulated in response to stress implies that these small RNAs have a role in stress tolerance. Stress-induced small RNAs might down-regulate their target genes, which may encode negative regulators of stress responses. Conversely, small RNAs down-regulated in response to stress cause the accumulation of their target mRNAs, which may contribute positively to the adaptation to stress. Here, we review the current status of small RNAs involved in biotic and abiotic stress regulatory networks.