Genome-wide identification of the MAPK gene family in peanut (Arachis hypogaea L.) and functional characterization of AhMPK3 and AhMPK18 in plant innate immunity

The mitogen-activated protein kinase (MAPK) cascade is a fundamental signaling module that translates environmental stimuli into cellular responses in eukaryotes. Despite its importance, a comprehensive analysis of this family in the allotetraploid peanut (Arachis hypogaea L.) remains limited.

In this study, 32 AhMAPK family members (AhMPK1-AhMPK32) were identified in the peanut genome. These genes are non-uniformly distributed across 14 chromosomes and are characterized by a widespread absence of introns. Phylogenetic analysis categorized the AhMPK proteins into four distinct subgroups (Groups I, II, III, and Ⅳ), with high conservation in gene structures and protein motifs within each group. Promoter analysis revealed an abundance of cis-acting elements responsive to light, phytohormones, and abiotic stresses. Transcriptomic profiling across 19 tissues and multiple stress conditions showed that while most AhMPK genes are constitutively expressed, AhMPK3 and AhMPK18 maintain high transcript abundance and are significantly induced by various environmental stimuli. Functional characterization through Agrobacterium-mediated transient and stable expression demonstrated that AhMPK3 and AhMPK18 positively regulate plant basal immunity. Overexpression of these genes significantly enhanced PAMP-induced reactive oxygen species (ROS) bursts, up-regulated the defense marker gene FRK1, and conferred increased resistance to Pseudomonas syringae pv. tomato (Pst) DC3000.

Collectively, our results provide a systematic genomic framework for the peanut AhMAPK family and identify AhMPK3 and AhMPK18 as critical candidates for the genetic improvement of disease resistance and stress resilience in peanut.