Department of Wood Science, University of British Columbia, Vancouver, BC V6T 1Z4, Canada.
Department of Biological Sciences, University of Toronto Scarborough, Toronto, ON M1C 1A4, Canada.
Plant Cell Physiol. 2021 Oct 1;62(5):827-838. doi: 10.1093/pcp/pcab040.
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.
角质层蜡由四个酶协同作用产生的非常长链脂肪酸（VLCFA）前体组成，这些酶形成脂肪酸（FA）延伸复合物。该复合物的缩合酶使不同链长的底物具有特异性，但仅凭自身不能解释长于 28 个碳原子（C28）的 VLCFA 的生物合成。最近来自拟南芥的证据表明，II 类 BAHD 酰基转移酶和缩合酶在 VLCFA 延伸超过 C28 方面具有协同作用。在毛白杨中，II 类由七个未鉴定的同源基因（PtCER2-like1-7）组成。在本研究中，这 5 个基因在酵母中异源表达，并确定了它们各自的 FA 图谱。PtCER2-like 以不同方式改变了 C28 和 C30 FA 的积累，当与缩合酶 AtCER6 一起表达时。在这些基因中，PtCER2-like5 在酵母中产生了最高水平的 C28 FA，其表达在 β-葡萄糖醛酸酶报告杨树系的表皮中定位，与角质层蜡生物合成的作用一致。用 PtCER2-like5 互补拟南芥 cer2-5 突变体增加了 C28 衍生的角质层蜡的水平，而牺牲了 C30 衍生的成分。这些结果共同表明，在杨树 II 类 BAHD 酰基转移酶中，CER2-like 在角质层蜡生物合成中的作用是保守的。
