Tomato KCS Gene Family Characterization and Response to Nitric Oxide During Drought Stress
3‐Ketoacyl‐CoA synthase ( KCS ) genes are essential for the biosynthesis of cuticular wax and very‐long‐chain fatty acids, which are key adaptation mechanisms for drought tolerance in plants. Nitric oxide (NO) is a well‐established signaling molecule implicated in plant abiotic stress responses, although its involvement in regulating KCS‐mediated wax biosynthesis during drought remains poorly understood. In this study, 21 SlKCS genes were identified in the tomato ( Solanum lycopersicum ) genome through genome‐wide analysis. These genes were unevenly distributed across 12 chromosomes, with six duplicated gene pairs evolving under strong purifying selection. Synteny analysis revealed greater collinearity with Glycine max than with the monocot Oryza sativa , consistent with the evolutionary divergence between dicot and monocot lineages. Promoter analysis identified 81 cis ‐regulatory elements, including 19 stress‐responsive motifs such as MYC, MYB, STRE, and ABRE, suggesting the involvement of SlKCS genes in abiotic stress responses. Based on these findings, the expression of four representative genes ( SlKCS5 , SlKCS7 , SlKCS12 , and SlKCS20 ) was examined under nitric oxide donor sodium nitroprusside (SNP), drought stress, and combined SNP + drought treatments, using qRT‐PCR. All four genes exhibited treatment‐dependent expression patterns, with SlKCS20 showing the strongest response, reaching approximately 58‐fold higher expression under drought stress. Drought stress also significantly increased cuticular wax accumulation in both leaves and stems, while combined SNP and drought treatment resulted in the greatest wax deposition, particularly in stems. These changes were accompanied by reduced leaf water loss, increased chlorophyll content, and partial recovery of the net photosynthetic rate under drought stress. Together, these findings suggest that exogenous SNP enhances drought tolerance by promoting cuticular wax accumulation and improving physiological performance, providing new insights into the role of SlKCS genes in drought adaptation.