Fine-tuning KCS3 and KCS12 activities in Arabidopsis is essential for maintaining cuticle integrity.

The cuticle, which consists of wax and cutin, is required for plant adaptations to various environments. β-Ketoacyl-CoA synthases (KCSs) usually serve as a component of the fatty acid elongation complex that participates in the production of very long-chain fatty acids and provides precursors for the synthesis of various lipids, including wax. However, we recently reported that KCS3 and KCS12 negatively regulate wax biosynthesis. In this study, we observed that unlike KCS3-overexpressing (OE) lines, KCS12 OE lines had fused floral organs because of abnormal cuticle biosynthesis. This compelled us to compare the functions of KCS3 and KCS12 during cuticle formation. The KCS3 mutation caused greater impacts on wax production, whereas the KCS12 mutation exerted severer effects on cutin synthesis. Mutations of both KCS12 and KCS3 significantly increased the wax and cutin contents to levels greater than those in either single mutant, suggesting that KCS12 and KCS3 have additive effects on cuticle biosynthesis. Cuticle permeability was greater for the double mutant than for the single mutants, which ultimately led to increased susceptibility to drought stress and floral organ fusion. Taken together, our study findings confirmed the regulatory roles of KCS3 and KCS12 during cuticle biosynthesis. Furthermore, maintaining KCS3 and KCS12 expression at certain levels is essential for the formation of a functional cuticle layer.