**7. Conclusion and future perspectives**

Above mentions exemplified case studies indicated that currently miRNAs viewed as a most essential gene regulator tool. This chapter also focused on the studies that describe the multipurpose role of miRNAs in plants. Recent advancement in biological science made to access and characterize miRNAs in crop plants, with a growing number of researches on the significant function of miRNAs [49]. As described, in plants few important processes like homeostasis, growth and development, vegetative to reproductive phase transition and signal transduction and response to various stress are regulated by miRNA [13]. Few recent studies also showed that in plants miRNAs biomolecule act as plant defense and organizers of immune responses [67]. In this regard, the supervision of miRNA expression levels would recognize a crucial way for enhancing the plant growth and development as well as various biotic and abiotic stresses tolerance.

Various transgenic approaches, focused on miRNA role and its importance and identification on corresponding target genes. These includes miRNA overexpression, tissue-specific expression of the targets or miRNAs or stress induce, artificial miRNA, expression of miRNA resistant target gene and artificial target mimic [68]. In cases where the natural target gene has a harmful effect on plant, the overexpression of the regulatory miRNA decreasing the corresponding mRNA expression [47]. Where the target gene has a positive effect, approaches tracked can involve the artificial target mimics or selection of miRNA resistant target gene and the overexpression of the target genes [37]. Although this approach generally successful, the applied agricultural application of the miRNA methods is interesting since the modification and alteration in complicated multi-genic traits such as productivity

may require alteration in expression of different genes during different developmental stages of plant. However, for improving crop stress tolerance several new strategies used for improving miRNA bases gene regulation in model plants [69].

It is also possible that few miRNAs affect expression of target gene only in some specific cell, and exclusively under specific environmental conditions as several miRNAs may have complicated expression pattern. In this circumstance, analysis of effect of miRNA on expression in whole organs would uncertain; therefore, the experiment should be specifically and carefully designed for improved results. Several artificial miRNAs designed and used to suppress expression of a target gene and protein-coding mRNA of interest is one of the among valuable and suitable approach for plant improvement [70]. Due to insufficient concentration and expression the effect of some crucial miRNAs may not visible in living tissue. For producing plants with desirable characters, it would be essential to execute some quantitative analysis of the natural miRNA(s) of the cells, before designing the artificial miRNAs.

Although, old artificial miRNA approach used as important tool for genetic modification [70], but still there is some more knowledge required for its appropriate use in the differentiation and translational inhibition by miRNA. Single miRNA produced by artificial nucleic acid with the ability to inhibit target loci, avoid and predict all the unnecessary genes for experiment design [52]. By modifying miRNA regulatory pathways, miRNA activity also altered for attaining a desired trait [71]. miRNA action negatively controlled by endogenous RNAs, it is a more flexible and fast way to understand the miRNA function, as well as for manipulation of target gene in plants [72]. This technique offers the way to attenuated miRNA inactivation by significant regulation of native miRNA targets and produce a wide range of phenotypes by change the miRNA decoy site sequence. However, for appropriate crop improvement and proper utilization of this approach, miRNA inactivation at appropriate level and to avoid off-site effects of miRNA which generate some false positive results [73]. Also, the interaction between miRNA and miRNA decoy, as well as the several complex produce by this interaction, is not well known and can causes the miRNA destabilization in organisms. Consequently, for the practical uses of this method in plants, some new and advance modification is needed on the procedure basic decoy-associated regulation of gene expression and miRNA turnover. miRNA and miRNA variants act as important tool in plant improvement, it is also nullifying the side effect produced accidently by genetic engineering technology [73]. If the targeted gene and expression of miRNA is modified, it can produce some pleiotropic alteration in plant development and morphogenesis. Therefore, it is very essential to recognize the miRNA regulation method for plant development, growth and plant responses to different biotic and abiotic stresses. This will simplify the plan of appropriate strategies resulting in the desired traits but with minimum trade-offs in the modified crops.

*microRNA Utilization as a Potential Tool for Stress Tolerance in Plants DOI: http://dx.doi.org/10.5772/intechopen.97480*
