Seminars

The outer epidermal cell walls of plant shoots are covered with a cuticle, a continuous lipid structure that protects plants from desiccation, UV-light, pathogens and insects. The cuticle is composed of cutin polymer matrix embedded and coated with wax. Cuticular wax consists predominantly of very-long-chain fatty acid (VLCFA) derivatives, ranging from 24-36 carbons in length. VLCFAs are synthesized by a fatty acid elongation (FAE) complex of four core enzymes located on the endoplasmic reticulum, which sequentially adds 2-carbon units to a growing acyl-CoA chain. The condensing enzyme of the FAE catalyzes the committed reaction of fatty acyl elongation and determines the length of fatty acyl chains accepted and produced by the complex. While critical for the elongation of VLCFA precursors of cuticular wax, characterized Arabidopsis condensing enzymes cannot efficiently produce VLCFAs longer than 28 carbons. This suggests that elongation beyond 28 carbons requires additional biosynthetic components.
We have taken advantage of the eceriferum2 (cer2) mutant of Arabidopsis that lacks wax components longer than 28 carbons to identify and functionally characterize a novel component of the elongation machinery involved in acyl chain extension past this threshold length. We have also characterized four CER2-LIKE genes from Arabidopsis, which together with CER2 form a distinct clade of the BAHD acyltransferase gene family. They encode proteins with similar metabolic functions to CER2 but have different expression patterns and substrate specificities. I will discuss the potential roles of CER2-LIKE proteins in fatty acid elongation of wax precursors.