Abstract
Millets are the strategic food crops in arid and drought-prone ecologies. Millets, by virtue of nature, are very well-adapted to drought conditions and able to produce sustainable yield. Millets have important nutrients that can help prevent micro-nutrient malnutrition. As a result of the adverse effect of climate change and widespread malnutrition, millets have attained a strategic position to sustain food and nutritional security. Although millets can adapt well to the drought ecologies where other cereals fail completely, the yield level is very low under stress. There is a tremendous opportunity to increase the genetic potential of millet crops in dry lands when the genetics of the drought-tolerance mechanism is fully explained. MicroRNAs (miRNAs) are the class of small RNAs that control trait expression. They are part of the gene regulation but little studied in millets. In the present study, novel miRNAs and gene targets were identified from the genomic resources of pearl millet, sorghum, foxtail millet, finger millet, and proso millet through in silico approaches. A total of 1,002 miRNAs from 280 families regulating 23,158 targets were identified using different filtration criteria in five millet species. The unique as well as conserved structural features and functional characteristics of miRNA across millets were explained. About 84 miRNAs were conserved across millets in different species combinations, which explained the evolutionary relationship of the millets. Further, 215 miRNAs controlling 155 unique major drought-responsive genes, transcription factors, and protein families revealed the genetics of drought tolerance that are accumulated in the millet genomes. The miRNAs regulating the drought stress through specific targets or multiple targets showed through a network analysis. The identified genes regulated by miRNA genes could be useful in developing functional markers and used for yield improvement under drought in millets as well as in other crops.
Highlights
MicroRNAs are small, single-stranded, non-coding, endogenous RNA of size varying from 21 to 24 nucleotides mainly involved in post-transcriptional gene regulation (Zhang et al, 2014; Aravind et al, 2017)
The homologous sequences were filtered by removing other RNA matches, which resulted in the removal of 8,173, 3,493, 771, 478, and 27 candidate sequences from finger miRNA-Regulated Drought Tolerance in Millets
Several miRNA families pre-date the divergence of gymnosperms and angiosperms (305 million years) and the divergence between vascular plants and mosses (490 million years). These results indicated that miRNA sequences are highly conserved across great phylogenetic distances and that similar selection pressures have been active in the regulation of gene expression in plant cells since the earliest stages of their evolution (Zhang et al, 2006)
Summary
MicroRNAs (miRNAs) are small, single-stranded, non-coding, endogenous RNA of size varying from 21 to 24 nucleotides mainly involved in post-transcriptional gene regulation (Zhang et al, 2014; Aravind et al, 2017). They are highly conserved in matured form, and the conserved nature has made it a molecule of interest in several plant growth, development, and stress regulatory studies without any species boundaries. This, coupled with miRNA– mRNA target interaction, results in overlapping functions of miRNAs belonging to the same families (Jones-Rhoades et al, 2006)
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