MiRNA-Based Biotechnology Approaches in Crop Response Improvement to Biotic Stress
RNA interference is a known phenomenon of plant immune responses, involving the regulation of gene expression. The key components triggering the silencing of targeted sequences are double-stranded RNA (dsRNA) or hairpin structured RNA (hpRNA) molecules. The regulation of host–pathogen interactions controlled by miRNA molecules, regulate the expression of host resistance genes or the genes of the pathogen. Short endogenous molecules of microRNA, resulting from hairpin-loop structures, have a significant regulatory potential. This epigenetic mechanism of gene regulation became a part of the contemporary research of host-pathogen interaction as well as a platform of environment friendly plant protection management.
Research has shown that miRNA molecules play an important role in the genome responses of plants to stress factors. Many stress-regulated genes have been found to be regulated by miRNAs []. Conserved classes of miRNA molecules have been identified that exhibit the same responses to biotic stress conditions in different plant species. Studies show that by regulating the expression of a particular type of miRNA molecule, plant tolerance or increase in tolerance to a defined stress factor may be enhanced or decreased []. For examples, the upregulation of miR393, miR319, miR156, and others was observed after infection of Arabidopsis leaves with P. syringae Pv. tomato []. The increased activity of miR393 induced by pathogen-mediated suppression of auxin receptors leads to enhanced resistance to bacterial infection [].
Several miRNAs have been identified that regulate viral resistance and, consequently, expression of virus-specific artificial miRNAs could provide novel approaches to crop resistance improvement [].
MicroRNA research has multiple applications in the field of plant biotechnology (a) in the form of molecular markers based on miRNA sequences or (b) in the form of molecular breeding based on miRNA molecules. In both cases, the goal is to improve plant characteristics and properties []. Currently, miRNA molecules are being addressed as biotechnological tools to improve plant biomass, crop, and tolerance to biotic and abiotic environmental factors []. This knowledge will be important in improving plant tolerance to environmental stress conditions and understanding plant responses to given molecular conditions.
Improvement of plant tolerance to biotic stress factors is necessary in order to ensure quality and safe food resources. Progress in this area is also determined by the extent to which we have identified the molecular mechanisms of resistance. As miRNAs are the key players in plant responses to pathogen attack, knowledge of their functional role and regulation of their expression will be able to improve crop tolerance to biotic stress factors (Figure 1).
Figure 1. Methodological platform of miRNA-based strategies in crop improvement to biotic stress factors. Note: NBS-LRR - nucleotide-binding site (NBS)–leucine-rich repeat (LRR).
In addition to high-throughput sequencing procedures, technologies for identifying the function of miRNA molecules and their target sequences include modifying miRNA expression by applying miRNA inhibitors and generating mutant plants carrying a non-functional MIR gene. Another strategy to study the function of individual miRNA molecules is to apply “artificial” miRNAs (amiRNAs, artificial miRNAs) []. These molecules are designed to specifically target mRNA expression. The use of artificial miRNAs designed to suppress target genes represents a valuable approach for crop improvement []. It has been shown that regulating the expression of a single miRNA can enhance or decrease plant tolerance to abiotic stress factors (e.g., drought, salinity) []. An integral part of microRNA research, so-called “miRNomics” involves computer approaches to function prediction using bioinformatics tools (in silico procedures).
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