Genome-wide identification of SERKs in four Gossypium species reveals GhBAK1 potentially promotes cotton defoliation

Cotton ( Gossypium spp.) holds significant global industrial importance as a primary textile fiber crop. Using chemical defoliants to speed up the shedding of leaves before machine harvesting is a necessary agricultural practice in cotton production. Somatic Embryogenesis Receptor Kinases (SERKs) have been reported to play roles in plant organ abscission. Still, SERK genes have not been fully studied in cotton, and whether cotton SERK genes respond to defoliant-induced abscission remains unknown. This study explores the biological roles of the SERK gene family in four cotton species ( G. arboreum , G. raimondii , G. barbadense , and G. hirsutum ), identifying 14,13, 22 and 26 SERK proteins, respectively. Phylogenetic analysis revealed three subfamilies of SERKs in cotton, with high homology within the subfamily suggesting similar biological functions among different cotton varieties. Expression profiling demonstrated distinct patterns of GhSERK genes in response to defoliant treatment in upland cotton. Functional studies demonstrated that GhSERK2–2 encoding brassinosteroid insensitive 1-associated kinase 1 (BAK1) plays a crucial positive role in leaf abscission, as evidenced by its upregulation following defoliant treatment and its involvement in brassinosteroid (BR) signaling pathways. Additionally, a hormone crosstalk network was constructed to elucidate the interactions between SERK genes and phytohormones in the defoliation process. These findings enhance our understanding of the functional diversity of SERK genes and their potential applications in improving cotton production efficiency. • Cotton SERK Genes: Found 14-26 SERK proteins in 4 cotton species, grouped into 3 highly homologous subfamilies, suggesting similar functional roles. • GhBAK1 & Leaf Abscission: GhBAK1 promotes cotton leaf shedding via brassinosteroid signaling, functionally confirmed. • Hormone Crosstalk: Mapped SERK-phytohormone interactions during defoliation, aiding strategies to boost cotton yield.