Enhanced osmotic adjustment, antioxidant defense, and photosynthesis efficiency under drought and heat stress of transgenic cowpea overexpressing an engineered DREB transcription factor

Abstract

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.