Transcriptomic Analysis of Drought Stress Response Mechanisms in Cowpea (Vigna unguiculata) Cultivars Adapted to Arid Zones of North West Nigeria

Cowpea (Vigna unguiculata) is an economically critical grain and vegetable legume in the arid zones of North West Nigeria, where seasonal drought is the primary abiotic stress limiting productivity. Understanding the molecular mechanisms underpinning drought tolerance in locally adapted cowpea cultivars is essential for rational breeding of drought-resilient genotypes suited to Nigerian production environments. This dissertation employs RNA-sequencing transcriptomics to profile the drought stress response of two drought-tolerant and two drought-sensitive cowpea cultivars sourced from Katsina and Zamfara states at three progressive stages of soil water deficit. Differentially expressed genes (DEGs) were identified using DESeq2, and enrichment analysis was performed to identify overrepresented biological processes and molecular functions under stress. Co-expression network analysis was applied using WGCNA to identify hub genes associated with drought tolerance. Over 4,800 DEGs were identified in tolerant cultivars relative to sensitive ones under severe stress, with significant enrichment in osmotic adjustment, reactive oxygen species scavenging, ABA signaling, and root architecture remodeling pathways. Hub gene analysis identified three novel transcription factor candidates in the MYB and DREB families as primary orchestrators of tolerance. These findings provide molecular targets for biotechnology-assisted cowpea improvement under Nigerian drought conditions. Keywords: cowpea, drought stress, transcriptomics, RNA-sequencing, North West Nigeria