MicroRNAs with macro-effects on plant stress responses

Being sessile organisms, plants often have to face challenges posed by environmental stresses. To minimize the cellular damage caused by stress, plants have evolved highly complex but well-coordinated adaptive responses operating at the transcriptional, post-transcriptional, translational and post-translational levels. A thorough understanding of regulation at all levels will provide better tools to improve plant's performance under stress. Dramatic changes in the levels of several hundreds or even thousands of mRNAs/proteins were evident under stress as revealed by high-throughput microarray and proteome analyses and such changes were thought to be dependent on transcriptional (induction or suppression of genes) or post-translational regulation (protein stability and degradation). However, recently discovered 21–24 nt small RNAs (microRNAs [miRNAs] and small-interfering RNAs [siRNAs]), which regulate gene expression at the post-transcriptional level, are also modulated during stress and possibly contribute to the stress-induced changes in profiles of mRNAs or proteins. This review highlights our understanding of the role of small RNAs in plant stress responses.