Sadhukhan, Ayan

MicroRNAs (miRNAs) are small, non-coding RNAs, 18–25 nt in length, that play a crucial role in regulating genes associated with the physiological processes and responses to various biotic and abiotic stresses. Different conserved and species-specific microRNAs and their functions have been identified, primarily in plants such as rice and Arabidopsis with sequenced genomes. Our present study identifies drought-responsive miRNAs and their potential targets from mungbean under three days of drought stress induced by PEG-6000. We constructed small RNA libraries from both control and drought-treated tolerant and susceptible mungbean genotypes and identified various miRNAs involved in drought stress regulation. Analysis of differentially expressed genes (DEGs) revealed 79 up-regulated and 158 down-regulated novel miRNAs and two up-and down-regulated known miRNAs under drought. Annotation of the miRNAs followed by target prediction and expression analysis revealed five miRNAs, Vra-miR160, Vra-miR164, Vra-miR167, Vra-miR394, and Vra-miR398, were potentially involved in the regulation of drought-responsive genes. Their predicted target genes were an Auxin response factor (ARF), a NAC (for petunia NAM and Arabidopsis ATAF1, ATAF2, and CUC2) transcription factor, Serine acetyltransferase 1, and Multicopper oxidase LPR2-like. The expression of drought-responsive miRNAs and their targets were validated by real-time PCR. Our data suggest that various known and novel microRNAs activated transcription factors, enzyme kinases, and hormone signaling pathways alleviate drought stress in the tolerant K-851 genotype of mungbean.

Cowpea is sensitive to drought and heat stress, particularly at the reproductive stages of development. Both stresses limit growth and yield, and their effect is more devastating when occurring concurrently. Dehydration-responsive element-binding protein 2A (DREB2A) is an important signaling hub integrating information about two different abiotic stresses, drought and heat. We identified VuDREB2A as a canonical DREB ortholog in cowpea, activating downstream stress-responsive genes by binding to DREs in their promoter. Post-translational modification of a negative regulatory domain (NRD) within the VuDREB2A protein prevents its degradation. Targeted deletion of the NRD produces a stable and constitutively active form VuDREB2A-CA. However, there is very little evidence of its practical utility under field conditions. This study overexpressed the VuDREB2A-CA in a popular cowpea variety and conducted drought- and heat-tolerance experiments across various stress regimes. Transgenic cowpea exhibited significant tolerance with consistently higher yield when exposed to over 30-d drought stress and 3-d exposure to high temperature (28 °C˗52 °C) without any pleiotropic alterations. The transgenic lines showed higher photosynthetic efficiency, osmotic adjustment, antioxidant defense, thermotolerance, and significantly higher survival and increased biomass than the wild type. Late embryogenesis abundant 5, heat shock protein 70, dehydrin, mitogen-activated protein kinase 2/4, isoflavonoid reductase, and myoinositol phosphate synthase were upregulated in transgenic lines under drought and heat stress. Through transcriptome analysis of the transgenic lines, we found significant up-regulation of various stress-responsive cowpea genes, having DRE in their promoter. Our results suggest that overexpression of VuDREB2A could improve cowpea production under drought and high temperatures.

Main Conclusion: Priestia species isolated from the cowpea rhizosphere altered the transcriptome of cowpea roots by colonization and enhanced nutrient uptake, antioxidant mechanisms, and photosynthesis, protecting cowpea from drought and nutrient deficiency. Abstract: Cowpea is a significant grain legume crop primarily grown in sub-Saharan Africa, Asia, and South America. Drought and nutrient deficiency affect the growth and yield of cowpea. To address this challenge, we studied the phyto-beneficial effects of stress-tolerant rhizobacteria on the biomass yield of cowpea under water- and nutrient-deficit conditions. Among the bacteria isolated, two rhizobacillus genotypes, C8 (Priestia filamentosa; basonym: Bacillus filamentosus) and C29 (Priestia aryabhattai; basonym: Bacillus aryabhattai) were evaluated for the improvement of seed germination and growth of cowpea under stress. Our study revealed that C8 protected cowpea from stress by facilitating phosphorus and potassium uptake, protecting it from oxidative damage, reducing transpiration, and enhancing CO2 assimilation. A 17% increase in root biomass upon C8 inoculation was concomitant with the induction of stress tolerance genes in cowpea roots predominantly involved in growth and metabolic processes, cell wall organization, ion homeostasis, and cellular responses to phosphate starvation. Our results indicate a metabolic alteration in cowpea root triggered by P. filamentosa, leading to efficient nutrient reallocation in the host plant. We propose inoculation with P. filamentosa as an effective strategy for improving the yield of cowpea in low-input agriculture, where chemical fertilization and irrigation are less accessible to resource-poor farmers.