Department of Plant Biology, Michigan State University, East Lansing, Michigan 48824, USA.
Plant Physiol. 2012 Sep;160(1):237-48. doi: 10.1104/pp.112.201822. Epub 2012 Jul 13.
While suberin is an insoluble heteropolymer, a number of soluble lipids can be extracted by rapid chloroform dipping of roots. These extracts include esters of saturated long-chain primary alcohols and hydroxycinnamic acids. Such fatty alcohols and hydroxycinnamic acids are also present in suberin. We demonstrate that alkyl coumarates and caffeates, which are the major components of Arabidopsis (Arabidopsis thaliana) root waxes, are present primarily in taproots. Previously we identified ALIPHATIC SUBERIN FERULOYL TRANSFERASE (At5g41040), a HXXXD-type acyltransferase (BAHD family), responsible for incorporation of ferulate into aliphatic suberin of Arabidopsis. However, aliphatic suberin feruloyl transferase mutants were unaffected in alkyl hydroxycinnamate ester root wax composition. Here we identify a closely related gene, At5g63560, responsible for the synthesis of a subset of alkyl hydroxycinnamate esters, the alkyl caffeates. Transgenic plants harboring P(At5g63560)::YFP fusions showed transcriptional activity in suberized tissues. Knockout mutants of At5g63560 were severely reduced in their alkyl caffeate but not alkyl coumarate content. Recombinant At5g63560p had greater acyltransferase activity when presented with caffeoyl-Coenzyme A (CoA) substrate, thus we have named this acyltransferase FATTY ALCOHOL:CAFFEOYL-CoA CAFFEOYL TRANSFERASE. Stress experiments revealed elevated alkyl coumarate content in root waxes of NaCl-treated wild-type and fatty alcohol:caffeoyl-CoA caffeoyl transferase plants. We further demonstrate that FATTY ACYL-CoA REDUCTASEs (FARs) FAR5 (At3g44550), FAR4 (At3g44540), and FAR1 (At5g22500) are required for the synthesis of C18, C20, and C22 alkyl hydroxycinnamates, respectively. Collectively, these results suggest that multiple acyltransferases are utilized for the synthesis of alkyl hydroxycinnamate esters of Arabidopsis root waxes and that FAR1/4/5 provide the fatty alcohols required for alkyl hydroxycinnamate synthesis.
尽管角质是一种不溶性杂聚物，但许多可溶性脂质可以通过快速氯仿浸渍根来提取。这些提取物包括饱和长链伯醇和羟基肉桂酸的酯。这些脂肪酸醇和羟基肉桂酸也存在于角质中。我们证明，烷基香豆素酯和咖啡酸酯是拟南芥（Arabidopsis thaliana）根蜡的主要成分，主要存在于主根中。之前，我们鉴定了 ALIPHATIC SUBERIN FERULOYL TRANSFERASE（At5g41040），一种 HXXXD 型酰基转移酶（BAHD 家族），负责将阿魏酸掺入拟南芥的脂肪角质中。然而，脂肪角质阿魏酰基转移酶突变体在烷基羟基肉桂酸酯根蜡组成中不受影响。在这里，我们鉴定了一个密切相关的基因 At5g63560，它负责合成一组烷基羟基肉桂酸酯，即烷基咖啡酸酯。携带 P（At5g63560）::YFP 融合的转基因植物在角质组织中表现出转录活性。At5g63560 的敲除突变体在其烷基咖啡酸酯但不是烷基香豆素酯含量上严重减少。当用咖啡酰辅酶 A（CoA）底物呈现时，重组 At5g63560p 具有更高的酰基转移酶活性，因此我们将这种酰基转移酶命名为脂肪酸醇：咖啡酰-CoA 咖啡酰转移酶。应激实验表明，在 NaCl 处理的野生型和脂肪酸醇：咖啡酰-CoA 咖啡酰转移酶植物的根蜡中，烷基香豆素酯的含量升高。我们进一步证明，脂肪酸酰基辅酶 A 还原酶（FARs） FAR5（At3g44550）、FAR4（At3g44540）和 FAR1（At5g22500）分别负责合成 C18、C20 和 C22 烷基羟基肉桂酸酯。总之，这些结果表明，多种酰基转移酶用于合成拟南芥根蜡的烷基羟基肉桂酸酯，并且 FAR1/4/5 提供了合成烷基羟基肉桂酸酯所需的脂肪酸醇。
