Nair Ramesh B, Bastress Kristen L, Ruegger Max O, Denault Jeff W, Chapple Clint
Department of Biochemistry, Purdue University, West Lafayette, Indiana 47907, USA.
Plant Cell. 2004 Feb;16(2):544-54. doi: 10.1105/tpc.017509. Epub 2004 Jan 16.
Recent research has significantly advanced our understanding of the phenylpropanoid pathway but has left in doubt the pathway by which sinapic acid is synthesized in plants. The reduced epidermal fluorescence1 (ref1) mutant of Arabidopsis thaliana accumulates only 10 to 30% of the sinapate esters found in wild-type plants. Positional cloning of the REF1 gene revealed that it encodes an aldehyde dehydrogenase, a member of a large class of NADP(+)-dependent enzymes that catalyze the oxidation of aldehydes to their corresponding carboxylic acids. Consistent with this finding, extracts of ref1 leaves exhibit low sinapaldehyde dehydrogenase activity. These data indicate that REF1 encodes a sinapaldehyde dehydrogenase required for sinapic acid and sinapate ester biosynthesis. When expressed in Escherichia coli, REF1 was found to exhibit both sinapaldehyde and coniferaldehyde dehydrogenase activity, and further phenotypic analysis of ref1 mutant plants showed that they contain less cell wall-esterified ferulic acid. These findings suggest that both ferulic acid and sinapic acid are derived, at least in part, through oxidation of coniferaldehyde and sinapaldehyde. This route is directly opposite to the traditional representation of phenylpropanoid metabolism in which hydroxycinnamic acids are instead precursors of their corresponding aldehydes.
近期的研究极大地推进了我们对苯丙烷类途径的理解，但植物中芥子酸的合成途径仍不明确。拟南芥的表皮荧光减弱1（ref1）突变体积累的芥子酸酯仅为野生型植物中芥子酸酯的10%至30%。REF1基因的定位克隆表明，它编码一种醛脱氢酶，醛脱氢酶是一大类依赖NADP(+)的酶的成员，这类酶催化醛氧化为相应的羧酸。与这一发现一致，ref1叶片提取物显示出较低的芥子醛脱氢酶活性。这些数据表明，REF1编码芥子酸和芥子酸酯生物合成所需的芥子醛脱氢酶。当在大肠杆菌中表达时，发现REF1同时具有芥子醛和松柏醛脱氢酶活性，对ref1突变体植物的进一步表型分析表明，它们含有的细胞壁酯化阿魏酸较少。这些发现表明，阿魏酸和芥子酸至少部分是通过松柏醛和芥子醛的氧化衍生而来。这条途径与苯丙烷类代谢的传统表述直接相反，在传统表述中，羟基肉桂酸是其相应醛的前体。
