Understanding the Role of Populus ECERIFERUM2-Likes in the Biosynthesis of Very-Long-Chain Fatty Acids for Cuticular Waxes

Cuticular waxes are derived from very-long-chain fatty acid (VLCFA) precursors made by the concerted action of four enzymes that form the fatty acid (FA) elongation complex. The condensing enzyme of the complex confers specificity to substrates of different chain lengths, yet on its own cannot account for the biosynthesis of VLCFAs longer than 28 carbons (C28). Recent evidence from Arabidopsis thaliana points to a synergistic role of clade II BAHD acyltransferases and condensing enzymes in the elongation of VLCFAs beyond C28. In Populus trichocarpa, clade II is composed of seven uncharacterized paralogous genes (PtCER2-like1-7). In the present study, five of these genes were heterologously expressed in yeast and their respective FA profiles were determined. PtCER2-likes differentially altered the accumulation of C28 and C30 FAs when expressed in the presence of the condensing enzyme AtCER6. Among these, PtCER2-like5 produced the highest levels of C28 FAs in yeast and its expression was localized to the epidermis in β-glucuronidase-reporter poplar lines, consistent with a role in cuticular wax biosynthesis. Complementation of the A. thaliana cer2-5 mutant with PtCER2-like5 increased the levels of C28-derived cuticular waxes at the expense of C30-derived components. Together, these results demonstrate that the role of CER2-likes in cuticular wax biosynthesis is conserved in Populus clade II BAHD acyltransferases.