Genome-wide analysis of KCS family in Medicago reveals MsKCS5's crucial role in abiotic stress adaptation.

Key message: Bioinformatics analysis identified 46 KCS genes in two Medicago species, linking their function to abiotic stresses with MsKCS5 enhancing yeast stress viability. The β-ketoacyl-CoA synthase (KCS) family, encoding pivotal rate-limiting enzymes for very-long-chain fatty acid biosynthesis, plays an indispensable role in plant cuticular wax formation. These hydrophobic layers constitute vital physical barriers that prevent water loss and pathogen penetration while simultaneously participating in stress signal transduction. Through comprehensive genome-wide analysis, 46 KCS genes were identified and characterized from two Medicago species: 19 in Medicago sativa and 27 in Medicago truncatula. Collinearity analysis further delineated the evolutionary trajectory of KCS genes, identifying tandem duplication events as a key driver of family diversification. Conserved motif architecture and exon-intron organization analyses demonstrated significant structural conservation within phylogenetic subgroups, suggesting functional coherence among paralogs. Promoter cis-element profiling uncovered an enrichment of stress-responsive and developmental regulatory motifs, aligning with the dual physiological roles of KCS genes. Transcriptomic analysis combined with RT-qPCR validation revealed differential expression patterns of alfalfa KCS members under drought, salinity, and cold stress, implicating their roles in abiotic stress adaptation. Subcellular localization assays via tobacco transient expression systems confirmed the plasma membrane targeting of MsKCS5, consistent with its putative function in extracellular wax deposition. Functional complementation assays in yeast heterologous expression systems revealed that MsKCS5 rescued stress-sensitive phenotypes, thereby verifying its conserved function in abiotic stress response mechanisms. This multi-omics framework elucidates the evolutionary dynamics and stress-responsive regulatory networks of KCS genes while identifying high-priority candidates for targeted genetic engineering to improve cuticular wax-mediated stress resilience in legume crops.