Role of microRNAs and other sRNAs of plants in their changing environments

Abstract

Plants constantly face a complex array of environmental biotic and abiotic stimuli. Recent studies in various plants have highlighted the key roles of microRNAs and of different siRNA classes in the post-transcriptional regulation of plant genes essential for conserved responses of plants to individual stress conditions. It is not yet clear how these different signals and responses are integrated in nature. In the present review, we summarize current knowledge on sRNA-mediated responses to stress, and highlight possible directions of future research.

Introduction

In nature, plants are exposed to a wide array of environmental stimuli and stresses that trigger various functional and/or structural responses. Plants are sessile organisms. They must cope with stressful environmental conditions, to integrate these various stresses and to adjust a proper molecular response that might eventually lead to their adaptation or acclimation to the stresses. A large proportion of plant genes are regulated by biotic (e.g. bacterial pathogen, virus, fungi, insects, nematodes, etc.) (Fagard et al., 2007, Brotman et al., 2012) and abiotic stresses (e.g. drought, soil salinity, extreme temperatures, heavy metals, etc.) (Chao et al., 2005, Si et al., 2009). These regulations potentially affect all the different levels of gene expression, i.e. transcription, RNA processing, translation or even posttranslational modifications.

RNA silencing encompasses a wide variety of mechanisms that commonly depend on guide RNA molecules. In plants, RNA silencing plays key roles in defense against viruses and in orchestrating the expression, stability, and inheritance of eukaryotic genomes (Chen, 2009, Vazquez et al., 2010). To reach these latter goals, plants have evolved a complex variety of small RNA (sRNA) regulators that control virtually every aspect of plant life. These sRNAs are generated through different pathways that depend on core highly conserved proteins of the DICER-LIKE, Double-strand RNA Binding, and ARGONAUTE family proteins (for details see Vazquez, 2006, Brodersen and Voinnet, 2006, Mallory and Vaucheret, 2010). sRNAs are called microRNAs when they are produced as discrete sRNA species from MIR genes and siRNAs when produced as complex sRNA pools from long dsRNA precursors.

MicroRNAs, trans-acting siRNAs and other siRNA species play crucial roles in plant development and act as bandmasters of genome expression. Several studies have also highlighted the key roles of these sRNA regulators in the post-transcriptional regulation of genes essential for plant response to various stress conditions. In this review, we summarize current knowledge on sRNA-mediated response to stress (Fig. 1, Table 1 and S1).