Completion of the core β-oxidative pathway of benzoic acid biosynthesis in plants
Completion of the core β-oxidative pathway of benzoic acid biosynthesis in plants
复制标题
DOI：
10.1073/pnas.1211001109
复制
发表时间：
2012-10-02
影响因子：
11.1
通讯作者：
Dudareva, Natalia
中科院分区：
文献类型：
--
作者：
Qualley, Anthony V.;Widhalm, Joshua R.;Dudareva, Natalia
尽管苯甲酸（BA）作为一系列初级和次级代谢产物的前体的重要性，但其在植物中的生物合成尚未完全阐明。由苯丙氨酸形成BA需要将C-3侧链缩短两个碳单元，这可以通过非β-氧化途径和/或类似于脂肪酸催化的β-氧化途径发生。负责核心BA β-氧化途径（肉桂酸->肉桂酰-CoA-> 3-羟基-3-苯丙酰-CoA-> 3-氧代-3-苯丙酰-CoA-> BA-CoA）的第一个和最后一个反应的酶先前已经在矮牵牛花（一种具有富含苯丙酸类/苯类挥发性化合物的花的植物）中表征。使用功能基因组学方法，我们已经确定了矮牵牛基因编码肉桂酰辅酶A水合酶-脱氢酶（PhCHD），一种双功能过氧化物酶体酶负责两个连续发生的未探索的中间步骤的核心BA β-氧化途径。PhCHD的空间，发育和时间共表达与已知的基因在BA β-氧化途径，并与苯挥发物的排放。重组PhCHD的动力学分析表明，它最有效地将肉桂酰辅酶A转化为3-氧代-3-苯丙酰辅酶A，从而形成该途径中最后一步的底物。在矮牵牛花中PhCHD表达的下调导致CHD酶活性降低，以及BA-CoA、BA及其衍生挥发物的形成减少。此外，转基因株系积累PhCHD底物肉桂酰辅酶A和上游途径中间体肉桂酸。PhCHD的发现完成了植物中核心BA β-氧化途径的阐明，并与先前表征的CoA连接酶和硫解酶一起提供了整个途径发生在过氧化物酶体中的证据。
Despite the importance of benzoic acid (BA) as a precursor for a wide array of primary and secondary metabolites, its biosynthesis in plants has not been fully elucidated. BA formation from phenylalanine requires shortening of the C-3 side chain by two carbon units, which can occur by a non-beta-oxidative route and/or a beta-oxidative pathway analogous to the catabolism of fatty acids. Enzymes responsible for the first and last reactions of the core BA beta-oxidative pathway (cinnamic acid -> cinnamoyl-CoA -> 3-hydroxy-3-phenylpropanoyl-CoA -> 3-oxo-3-phenylpropanoyl-CoA -> BA-CoA) have previously been characterized in petunia, a plant with flowers rich in phenylpropanoid/benzenoid volatile compounds. Using a functional genomics approach, we have identified a petunia gene encoding cinnamoyl-CoA hydratase-dehydrogenase (PhCHD), a bifunctional peroxisomal enzyme responsible for two consecutively occurring unexplored intermediate steps in the core BA beta-oxidative pathway. PhCHD spatially, developmentally, and temporally coexpresses with known genes in the BA beta-oxidative pathway, and correlates with emission of benzenoid volatiles. Kinetic analysis of recombinant PhCHD revealed it most efficiently converts cinnamoyl-CoA to 3-oxo-3-phenylpropanoyl-CoA, thus forming the substrate for the final step in the pathway. Down-regulation of PhCHD expression in petunia flowers resulted in reduced CHD enzyme activity, as well as decreased formation of BA-CoA, BA and their derived volatiles. Moreover, transgenic lines accumulated the PhCHD substrate cinnamoyl-CoA and the upstream pathway intermediate cinnamic acid. Discovery of PhCHD completes the elucidation of the core BA beta-oxidative route in plants, and together with the previously characterized CoA-ligase and thiolase enzymes, provides evidence that the whole pathway occurs in peroxisomes.