Characterization of SRC2 Genes in Cotton Identifies the Role of GhSRC2 ‐ 3D in Verticillium dahliae Resistance in Upland Cotton

Verticillium wilt, primarily caused by Verticillium dahliae , represents a major constraint on both quality and yield in upland cotton ( Gossypium hirsutum ). Calcium (Ca 2+ ) functions as a pivotal second messenger in plant signal transduction, regulating the expression of stress‐induced genes. The Soybean gene Regulated by Cold‐2 (SRC2), which encodes a protein containing C2 domains, is known to play important roles in plant development and environmental adaptation. In this study, a total of 31 SRC2 members were identified in five cotton species and classified into five distinct groups. Analyses of gene structure and conserved protein motifs revealed that SRC2 genes are evolutionarily conserved. GhSRC2 genes were widely expressed in various cotton tissues and showed responsiveness to cold, heat, drought and salt stresses. Notably, GhSRC2‐3D expression was significantly induced upon V. dahliae infection. Subcellular localization assays indicated that GhSRC2‐3D localizes to the cell membrane. Complementation of Arabidopsis src2 mutant with GhSRC2‐3D restored resistance to V. dahliae , while a C2 domain deletion variant (ΔGhSRC2‐3D) failed to confer resistance. Furthermore, down‐regulation of GhSRC2‐3D mediated by virus‐induced gene silencing (VIGS) compromised V. dahliae resistance in upland cotton. Collectively, our findings demonstrate the conserved role of GhSRC2‐3D in plant defense against V. dahliae infection and underscore the essential contribution of its C2 domain to protein function.