The Attributes of RNA Interference in Relation to Plant Abiotic Stress Tolerance
RNA interference has become a new paradigm for understanding gene regulation. It is a highly conserved process which functions in a very sequence specific manner and induce gene silencing. The mechanism of action involves depletion and subsequent degradation of targeted mRNA by introducing double stranded RNA thereby inhibiting the expression of corresponding gene specifically and efficiently. RNAi is a very common phenomenon which was initially discovered in plants and then in nematode, flies, zebra fish and mammalian cells. It has emerged as an indispensible tool for loss of gene function studies across the eukaryotic world.
There are several classes of small non coding RNAs that can regulate gene by targeting transcripts in the cytoplasm and repressing their translation. In plants, based on their biogenesis, functional categorization and the structure of genomic loci from which they are transcribed small regulatory RNAs can be classified into two major classes. The micro RNAs (miRNA) and the small interfering RNAs (siRNA). The main distinguishing features between miRNAs and siRNAs is the number of short RNA molecules generated from one loci.
In case of miRNAs only one miRNA duplex is produced from one miRNA loci whereas many siRNA duplexes are generated from one siRNA loci. Another distinct character that differentiates siRNAs from miRNAs is that they are generated from long double stranded RNA molecules by the action of RNA dependant RNA polymerase. These small non coding RNAs have been found to affect various biological processes such as leaf morphogenesis, root development, and floral organ identity. Their roles in response to different abiotic and biotic stresses have also been studied by several workers
Plant Micro RNA Biogenesis and mechanism of its action: Micro RNAs are 20-24 nucleotide long non coding RNAs encoded by miRNA genes that are transcribed into primary miRNAs by RNA polymerase II which in turn is converted into precursor miRNA, a self-complementary stem loop secondary structure that often exhibit an imperfect double stranded character. These precursor miRNA gives rise to the mature miRNA duplex by the action of dicer like (DCL) protein.
Micro RNAs: Attributes in Plant Abiotic Stress responses: Plants combat environmental stresses by activating several gene regulatory pathways. Plant exposed to abiotic stress causes over or under expression of certain miRNA and might even lead to the synthesis of new miRNAs to withstand stress
Superoxide in plants that causes oxidative damage is converted into less toxic hydrogen peroxide and molecular oxygen by the enzyme superoxide dismutase (SOD). This is one of the most important enzymes involved in the ROS scavenging system. Cu-Zn SODs are encoded by CSD1, CSD2 and CSD3 in Arabidopsis and miR398 was predicted to target these genes.
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