Department of Botany, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada.
Department of Chemistry, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada.
Plant Physiol. 2021 Aug 3;186(4):1812-1831. doi: 10.1093/plphys/kiab182.
Monounsaturated alkenes are present in the cuticular waxes of diverse plants and are thought to play important roles in their interactions with abiotic and biotic factors. Arabidopsis (Arabidopsis thaliana) leaf wax has been reported to contain alkenes; however, their biosynthesis has not been investigated to date. Here, we found that these alkenes have mainly ω-7 and ω-9 double bonds in characteristically long hydrocarbon chains ranging from C33 to C37. A screening of desaturase-deficient mutants showed that a single desaturase belonging to the acyl-CoA desaturase (ADS) family, previously reported as ADS4.2, was responsible for introducing double bonds en route to the wax alkenes. ADS4.2 was highly expressed in young leaves, especially in trichomes, where the alkenes are known to accumulate. The enzyme showed strong activity on acyl substrates longer than C32 and ω-7 product regio-specificity when expressed in yeast (Saccharomyces cerevisiae). Its endoplasmic reticulum localization further confirmed that ADS4.2 has access to very-long-chain fatty acyl-CoA substrates. The upstream biosynthesis pathways providing substrates to ADS4.2 and the downstream reactions forming the alkene products in Arabidopsis were further clarified by alkene analysis of mutants deficient in other wax biosynthesis genes. Overall, our results show that Arabidopsis produces wax alkenes through a unique elongation-desaturation pathway, which requires the participation of ADS4.2.
单不饱和烯在多种植物的角质层蜡中存在，被认为在其与非生物和生物因素的相互作用中发挥重要作用。已报道拟南芥（Arabidopsis thaliana）叶蜡中含有烯；然而，迄今为止尚未研究其生物合成。在这里，我们发现这些烯具有主要的 ω-7 和 ω-9 双键，其特征在于从 C33 到 C37 的长烃链中。对去饱和酶缺陷突变体的筛选表明，属于酰基辅酶 A 去饱和酶（ADS）家族的单个去饱和酶，先前报道为 ADS4.2，负责在蜡烯的形成过程中引入双键。ADS4.2 在幼叶中高度表达，特别是在毛状体中，已知烯类物质在毛状体中积累。该酶在酵母（酿酒酵母）中表达时对长于 C32 的酰基底物表现出强烈的活性和 ω-7 产物区域特异性。其内质网定位进一步证实 ADS4.2 可以接触到非常长链脂肪酸酰基辅酶 A 底物。通过对其他蜡生物合成基因缺陷突变体的烯分析，进一步阐明了为 ADS4.2 提供底物的上游生物合成途径和在拟南芥中形成烯产物的下游反应。总的来说，我们的结果表明，拟南芥通过独特的伸长-去饱和途径产生蜡烯，该途径需要 ADS4.2 的参与。
