Role of Microrna in Plant Stress Response
Authors: J. Vanitha, J. Srinivasan and R. Mahendran
A microRNA molecule has very few nucleotides (an average of 22) compared with other RNAs. miRNAs are post-transcriptional regulators that bind to complementary sequences on target messenger RNA transcripts (mRNAs), usually resulting in translational repression or target degradation and gene silencing. The human genome may encode over 1000 miRNAs, which may target about 60% of mammalian genes and are abundant in many human cell types. Different sets of expressed miRNAs are found in different cell types and tissues.
miRNAs in plant stress
Plants exposed to stress use multiple gene regulatory mechanisms, including post-transcriptional regulation of gene expression, to restore and re-establish cellular homeostasis. miRNAs have emerged as ubiquitous post-transcriptional gene regulatory molecules in plants and animals. Plant miRNAs are approximately 21 nucleotide long small regulatory RNAs that are derived from the processing of longer primary miRNA transcripts adopting hairpin-like structures.
Although miRNAs are small in number, the overall impact of miRNA-controlled gene regulation in plants cannot be underestimated because most of the target mRNAs are transcription factors. These transcription factors can potentially participate in most developmental processes from seed germination to seed maturation. Thus, miRNAs are thought to regulate primarily developmental processes. However, a direct link between miRNAs and plant stress responses has emerged with the identification of miR398, which targets two Cu/Zn superoxide dismutases (CSD1 and CSD2), and miR395 and miR399, which target the sulfate transporter (AST68) and the phosphate transporter (PHO1), respectively. miRNAs and plant stress responses may also be linked by the fact that hyl1 and cap-binding protein 80/ABA HYPERSENSITIVE 1 (cbp80/abh1) mutants that are compromised in miRNA biogenesis are hypersensitive to ABA, a modulator of the expression of several stress-responsive genes. Even more striking is the fact that the profile of most conserved miRNAs that target transcription factors are significantly altered in response to stress. Even subtle and transient changes in miRNA expression during stress can have profound physiological effects. For instance, miR393 is upregulated slightly and transiently in response to nitrogen availability, but can have a robust effect on root architecture by regulating the abundance of AFB3 mRNA. Similarly, there is a subtle and transient change in miR393 expression in leaves challenged with flg-22 (Pseudomonas syringae pv. tomato DC3000 flagellin derived peptide) that suggests a role for miR393 in plant disease resistance. Indeed, transgenic plants over expressing miR393, in which transport inhibitor response1 (TIR1) transcript levels are decreased, exhibit enhanced resistance to bacterial infection.
Plant growth and development are attenuated during stress but relatively little is known about how this is achieved at the molecular level. miRNAs recognize their mRNA targets based on imperfect sequence complementary and suppress expression of the target gene by guiding degradation and/or translational repression of the cognate mRNA target. In addition to discussing recent findings that have enhanced our understanding of the role of miRNAs during stress, this topic highlights the importance of miRNAs that have emerged as molecular links between modulation of plant growth and development.
About Author / Additional Info:
I have finished my PhD in Plant Breeding and Genetics (TNAU, Coimbatore). Currently working as assistant professor in Sethu Bhaskara Agricultural College and Research Foundation, Karaikudi