Genome‐wide identification and expression analysis reveals the drought‐response MAPK genes in peanut ( <i>Arachis hypogaea</i> L.)

Peanut (Arachis hypogaea L.) is one of the most important oilseed and food crops, and the drought stress remains the primary adverse environmental factor limiting its growth and productivity. Mitogen-activated protein kinase (MAPK) cascades play crucial roles in various signal transduction pathways, affecting a wide range of physiological processes and drought stress responses in plants; however, the systematic analysis of the MAPK gene family in peanuts remains unexplored. In this study, we identified 30, 16, and 15 MAPK genes in A. hypogaea, Arachis duranensis, and Arachis ipaensis, respectively. RNA-sequencing analysis in drought-tolerant and drought-susceptible genotypes revealed that Ah_At_MAPK4 and Ah_Bt_MAPK4 were significantly upregulated under drought stress conditions, with substantially higher induction in drought-tolerant genotypes compared to drought-susceptible ones. Weighted gene co-expression network analysis further identified a drought-responsive turquoise module highly correlated with drought tolerance traits, and both Ah_At_MAPK4 and Ah_Bt_MAPK4 were identified as core regulatory components within this module. Hub gene analysis revealed these MAPKs co-express with calmodulin-binding proteins, implicating calcium signaling in drought adaptation. Three-dimensional structural modeling confirmed both proteins possess canonical bilobed kinase architecture with properly positioned Thr-Glu-Tyr motifs and intact catalytic machinery. This genome-to-structure analysis identifies Ah_At_MAPK4 and Ah_Bt_MAPK4 as key components in drought-responsive networks and provides molecular targets for enhancing drought resilience in peanut breeding.