Plant miRNAome: Cross Talk in Abiotic Stressful Times

Abstract

The “small RNA world” discovered by plant biologists has acquired a central, regulatory role in diverse and fundamental processes including genome stability, gene expression and defense. The microRNAs (miRNAs) are a group of small noncoding RNAs found in both animals and plants. Since their discovery in Arabidopsis thaliana, plant miRNAs have been identified and their target genes are characterized in various plant species. While some miRNAs are functionally conserved across plant species, studies have also shown that miRNAs respond to environmental stresses in a stress-, tissue-, and genotype-dependent manner. During abiotic stress, miRNAs function by regulating target genes within the miRNA–target gene network and by controlling signaling pathways. Both stress-induced and stress-inhibited miRNAs constitute a controlling mechanism for fine tuning the positive or negative regulators of different stress-regulated pathways. These properties suggest that miRNA-based genetic modifications have the potential to enhance abiotic stress tolerance in crops. Furthermore, consequent to stress perception, epigenetic changes facilitate miRNA regulation of several transcription factors, which are common to drought, salt and heavy metal stress. With the rapid advancement in methods of whole genome sequencing, several new and novel miRNAs are being identified and research efforts are underway to decipher the “microRNAome”—a comprehensive view of miRNA-mediated gene regulatory networks in plants. The horizon of ‘regulatory RNA’ field is expanding, and new developments will certainly enhance our understanding of microRNA interactome under stress conditions. In this article, we discuss the perspective of microRNA regulation of salt, drought and heavy metal stress with an emphasis on shared mechanisms and provide an understanding of their potential roles in plant adaptation to abiotic stress conditions.