Understanding NAC transcription Factor Mediated signaling in the Regulation of Growth and Abiotic Stress Tolerance in Cowpea

Abstract

Abiotic stresses such as drought, salinity, and heat, account for ≥ 50% yield loss. NAC transcription factors (TFs) have emerged as a powerful tool to manipulate central stress-signaling. However, the functional conservation of orthologous NAC genes is unpredictable, limiting their use in pulse genetic-engineering. Besides, transcriptional-reprogramming of stress-responses often cause yield-penalty. My Ph.D. thesis provides unique and strategic translational tool to develop stress-tolerance and yield improvement in pulses without growth trade-off. A genome-wide analysis was performed to annotate the unexplored NAC family in cowpea (VuNAC), which is an important pulse crop. The in-silico promoter analysis and integrative gene regulatory network (iGRN) indicated their crucial role in both stress and growth responses, governed by multi-tier signaling comprising of light, phytohormones, sugar, micronutrient, and stress-factors. Two potential genes (VuNAC1 and VuNAC2) were cloned for molecular and biological functional study. The nuclear localization, DNA-binding assay, yeast-one and two hybrid, demonstrated the transactivation and dimerization abilities of the proteins. The genes showed prominent induction by dehydration, osmotic-stress, NaCl, aluminum, heat, cold, abscisic acid (ABA), methyl-jasmonate. The heterologous expression in yeast conferred tolerance to multiple stresses, improved cell-proliferation, longevity, and metabolic remodeling of vital energy-generating pathways, such as biosynthesis of ATP, vitamin B complex, methionine, and glutathione, giving preliminary insight into unique and versatile functions of VuNAC1/2. When expressed in Arabidopsis, the transgenic lines exhibited reduced ABA-hypersensitivity, enhanced growth and photosynthesis, and tolerance to severe drought, salinity, aluminum, cadmium, and H2O2 toxicity, under optimum and nutrient-deficit conditions.