Arabidopsis ketoacyl-CoA synthase 16 (KCS16) forms C36/C38 acyl precursors for leaf trichome and pavement surface wax

The aliphatic waxes sealing plant surfaces against environmental stress are generated by fatty acid elongase complexes, each containing a beta-ketoacyl-CoA synthase (KCS) enzyme that catalyses a crucial condensation forming a new C-C bond to extend the carbon backbone. The relatively high abundance of C-35 and C-37 alkanes derived from C-36 and C-38 acyl-CoAs in Arabidopsis leaf trichomes (relative to other epidermis cells) suggests differences in the elongation machineries of different epidermis cell types, possibly involving KCS16, a condensing enzyme expressed preferentially in trichomes. Here, KCS16 was found expressed primarily in Arabidopsis rosette leaves, flowers and siliques, and the corresponding protein was localized to the endoplasmic reticulum. The cuticular waxes on young leaves and isolated leaf trichomes of ksc16 loss-of-function mutants were depleted of C-35 and C-37 alkanes and alkenes, whereas expression of Arabidopsis KCS16 in yeast and ectopic overexpression in Arabidopsis resulted in accumulation of C-36 and C-38 fatty acid products. Taken together, our results show that KCS16 is the sole enzyme catalysing the elongation of C-34 to C-38 acyl-CoAs in Arabidopsis leaf trichomes and that it contributes to the formation of extra-long compounds in adjacent pavement cells.