Acetyl-CoA Carboxylase1 Influences ECERIFERUM2 Activity to Mediate the Synthesis of Very-Long-Chain Fatty Acid Past C28.

Abstract

Cuticular wax is a protective layer on the aerial surfaces of land plants. In Arabidopsis (Arabidopsis thaliana), cuticular wax is mainly constituted of compounds derived from very-long-chain fatty acids (VLCFAs) with chain lengths longer than C28. CER2-LIKE (ECERIFERUM2-LIKE) proteins interact with CER6/KCS6 (ECERIFERUM6/β-Ketoacyl-CoA Synthase6), the key enzyme of the fatty acid elongase complex, to modify its substrate specificity for VLCFA elongation past C28. However, the molecular regulatory mechanism of CER2-LIKE proteins remains unclear. Arabidopsis eceriferum19 (cer19) mutants display wax-deficient stems caused by loss of waxes longer than C28, indicating that CER19 may participate in the CER2-LIKE-mediated VLCFA elongation past C28. Using positional cloning and genetic complementation, we showed that CER19 encodes Acetyl-CoA Carboxylase1 (ACC1), which catalyzes the synthesis of malonyl-CoA, the essential substrate for the CER6/KCS6-mediated condensation reaction in VLCFA synthesis. We demonstrated that ACC1 physically interacts with CER2-LIKE proteins via split-ubiquitin yeast two-hybrid (SUY2H) and firefly luciferase complementation imaging (LCI) analysis. Additionally, heterologous expression in yeast and genetic analysis in Arabidopsis revealed that ACC1 affects CER2 activity to influence VLCFA elongation past C28. These findings imply that CER2-LIKE proteins might function as a link between ACC1 and CER6/KCS6 and subsequently enhance CER6/KCS6 binding to malonyl-CoA for further utilization in VLCFA elongation past C28. This information deepens our understanding of the complex mechanism of cuticular wax biosynthesis.