A 3‑Ketoacyl-CoA Synthase 10 (<i>KCS10</i>) Homologue from Alfalfa Enhances Drought Tolerance by Regulating Cuticular Wax Biosynthesis

Cuticular wax, forming the first line of defense against adverse environmental stresses, comprises very long-chain fatty acids (VLCFAs) and their derivatives. 3-Ketoacyl-CoA synthase (KCS) is a rate-limiting enzyme for VLCFA biosynthesis. In this study, we isolated <i>KCS10</i>, a <i>KCS</i> gene from alfalfa, and analyzed the effect of gene expression on wax production and drought stress in transgenic plants. <i>MsKCS10</i> overexpression increased compact platelet-like crystal deposition and promoted primary alcohol biosynthesis through acyl reduction pathways in alfalfa leaves. Overexpression of <i>MsKCS10</i> induced the formation of coiled-rodlet-like crystals and increased <i>n</i>-alkane content through decarbonylation pathways in tobacco and tomato fruits. Overexpression of <i>MsKCS10</i> enhanced drought tolerance by limiting nonstomatal water loss, improving photosynthesis, and maintaining osmotic potential under drought stress in transgenic tobacco. In summary, <i>MsKCS10</i> plays an important role in wax biosynthesis, wax crystal morphology, and drought tolerance, although the mechanisms are different among the plant species. <i>MsKCS10</i> can be targeted in future breeding programs to improve drought tolerance in plants.