“Employing miRNA for crop improvement”

       The Indian agriculture system faces various challenges that impact its productivity, sustainability, and the livelihoods of millions of farmers. The conventional plant breeding has been a cornerstone of agricultural progress for centuries. However, agriculture productivity is always threatened by many biotic and abiotic stresses. To overcome this situation, development of stress resistance and high yielding crop varieties through genetic manipulation can be a fast adopted option. MicroRNAs (miRNAs) are small RNA molecules that play a crucial role in the post-transcriptional regulation of gene expression in plants and animals. In the context of crop improvement, employing microRNAs holds significant potential for various applications. miRNA targets many transcription factor proteins contributing for increased biomass, nutritional quality, fruit quality, shelf life, biotic and abiotic stress resistance. Further miPEPs belong to non-conventional peptides that are an important tool of present research in various crop improvement programs that could be exploited such that it surpass strict transgenic control rules.

miRNAs are synthesized by RNA-Pol II from non-coding regions of DNA, transcribed into primary-miRNA (pri-miRNA) which processed by DCL1 in coordination with HYL1, SE1 to form miRNA:miRNA*duplex. Further this duplex is loaded onto RISC complex consisting of Argonaute (AGO1) protein in the cytoplasm that targets mRNA strand and resulting in down regulation of target gene2.

Sucking pests like the whitefly (Bemisia tabaci), miRNA is clearly involved in controlling gene expression linked to pest resistance through the amiRNA strategy. Three essential genes- Sex-lethal (Sxl), acetylcholinesterase (AChE), and orcokinin (Orc) were chosen to create an amiRNAWF construct, which significantly monitors whitefly3.

Overexpression of novel tobacco miRNA nta-miRX27 that downregulates QPT2, thus reducing the nicotine content. The insertion of noncleavable endogenous target mimicry (eTM) - nta-STTMX27 that reduces the expression of miRNA nta-miRX27 resulting in the improvement of nicotine content in tobacco1.

The use of microRNA (miRNAs) in genetic engineering to enhance agricultural traits is gaining attention. The effective use of miRNA in the molecular crop breeding field to take advantage of high yielding, stress-tolerant crop plants would improve our capacity to deal with upcoming global food insecurity issues, having still many unanswered questions provide scope for exploring miRNA applications. While the potential benefits are promising, challenges related to technology, ethics, and regulations must be addressed. Ongoing research seeks to deepen our understanding of miRNA functions and optimize their application in agricultural biotechnology, ensuring safe and effective integration into crop improvement strategies.

References: 

1 LI, F., WANG, W., ZHAO, N., XIAO, B., CAO, P., WU, X., YE, C., SHEN, E., QIU, J., ZHU, Q.H. AND XIE, J., 2015, Regulation of nicotine biosynthesis by an endogenous target mimicry of microRNA in tobacco. Plant Physiol., 169(2): 1062-1071.

 2 TANG, J. AND CHU, C., 2017, MicroRNAs in crop improvement: fine-tuners for complex traits. Nat. Plants, 3(7): 1-11. 

3 ZUBAIR, M., KHAN, M.Z., RAUF, I., RAZA, A., SHAH, A.H., HASSAN, I., AMIN, I. AND MANSOOR, S., 2020, Artificial micro-RNA (amiRNA)-mediated resistance against whitefly (Bemisia tabaci) targeting three genes. Crop Prot., 137: 105308.