3‐ketoacyl‐CoA synthase 19 contributes to the biosynthesis of seed lipids and cuticular wax in Arabidopsis and abiotic stress tolerance.

Very‐long‐chain fatty acids (VLCFAs) are essential precursors for plant membrane lipids, cuticular waxes, suberin, and storage oils. Integral to the fatty acid elongase (FAE) complex, 3‐ketoacyl‐CoA synthases (KCSs) function as crucial enzymes in the VLCFA pathway, determining the chain length of VLCFA. This study explores the in‐planta role of the <italic>KCS19</italic> gene. <italic>KCS19</italic> is predominantly expressed in leaves and stem epidermis, sepals, styles, early silique walls, beaks, pedicels, and mature embryos. Localized in the endoplasmic reticulum, KCS19 interacts with other FAE proteins. <italic>kcs19</italic> knockout mutants displayed reduced total wax and wax crystals, particularly alkanes, while <italic>KCS19</italic> overexpression increased these components and wax crystals. Moreover, the cuticle permeability was higher for the <italic>kcs19</italic> mutants compared to the wild type, rendering them more susceptible to drought and salt stress, whereas <italic>KCS19</italic> overexpression enhanced drought and salt tolerance. Disrupting <italic>KCS19</italic> increased C18 species and decreased C20 and longer species in seed fatty acids, indicating its role in elongating C18 to C20 VLCFAs, potentially up to C24 for seed storage lipids. Collectively, KCS19‐mediated VLCFA synthesis is required for cuticular wax biosynthesis and seed storage lipids, impacting plant responses to abiotic stress. [ABSTRACT FROM AUTHOR]