Identification of Tomato KCS Gene Family and Its Role in Nitric Oxide-Enhanced Cuticular Wax Accumulation under Drought Stress

The accumulation of cuticular wax, composed of very long-chain fatty acids (VLCFA), on leaf surfaces is one of the critical drought stress responses in plants. 3-ketoacyl-CoA synthase (KCS) is among the main enzyme families involved in the VLCFA biosynthesis. Nitric oxide (NO) is shown to be involved in reducing post-harvest losses in pear by promoting cuticular wax formation. However, the effect of NO in modulating the expression of the KCS gene family under drought stress and the resultant changes in wax biosynthesis and drought stress response have not been investigated in Solanum lycopersicum . The current study was designed to carry out in silico identification and characterization of the KCS gene family in S. lycopersicum , and to evaluate the effect of NO donor sodium nitroprusside (SNP) on the expression of KCS genes and wax accumulation under drought stress. A total of 21 KCS genes were identified in the tomato genome, distributed across 12 chromosomes and exhibiting distinct evolutionary patterns from monocots. Promoters of SlKCS genes were enriched with cis -acting regulatory elements linked to abiotic stress and hormone signaling. Semi-quantitative PCR results revealed that SNP treatment enhanced the expression of selected SlKCS genes under drought stress. This subsequently led to a significant increase in wax load and improved drought tolerance as manifested by reduced water loss from leaves and better photosynthesis efficiency under drought stress. These findings may help to deepen our understanding of the role of NO in the regulation of wax biosynthesis and subsequent drought stress response in plants.