PBS3 and EPS1 Complete Salicylic Acid Biosynthesis from Isochorismate in Arabidopsis
PBS3 and EPS1 Complete Salicylic Acid Biosynthesis from Isochorismate in Arabidopsis
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DOI：
10.1016/j.molp.2019.11.005
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发表时间：
2019-12-02
期刊：
影响因子：
27.5
通讯作者：
Weng, Jing-Ke
中科院分区：
文献类型：
--
作者：
Torrens-Spence, Michael P.;Bobokalonova, Anastassia;Weng, Jing-Ke
水杨酸（SA）是一种重要的植物激素，在植物体内既可调节局部防御反应，也可调节系统防御反应。尽管经过了半个多世纪的研究，植物如何生物合成SA仍然没有得到解决。在拟南芥中，SA的主要部分来源于异分支酸，异分支酸是由异分支酸合成酶产生的关键中间体，这让人想起细菌中的SA生物合成。而细菌采用异分支酸丙酮酸裂解酶（IPL），催化的周转异分支酸丙酮酸和SA，植物不包含IPL的直系同源物，并产生SA从异分支酸通过一个未知的机制。结合遗传学和生物化学方法，我们描绘了异分支酸下游的SA生物合成途径在拟南芥。我们发现PBS 3是一种对SA积累很重要的GH 3酰基腺苷酸酶家族酶，它催化L-谷氨酸主要与异分支酸的8-羧基的ATP和Mg 2+依赖性缀合，并产生关键的SA生物合成中间体异分支酰谷氨酸A。此外，我们发现，EPS 1，BAHD酰基转移酶家族蛋白与以前牵连的作用，SA积累病原体攻击后，窝藏一个非典型的活性位点和前所未有的异chorismoyl-谷氨酸A乙酰谷氨酸裂解酶活性，产生SA从异chorismoyl-谷氨酸A底物。PBS 3和EPS 1共同形成了一个两步代谢途径，以在拟南芥中从异分支酸产生SA，这与SA在细菌中的生物合成方式不同。这项研究填补了植物SA代谢方面的一个主要知识空白，将有助于开发作物抗病工程的新策略。
Salicylic acid (SA) is an important phytohormone mediating both local and systemic defense responses in plants. Despite over half a century of research, how plants biosynthesize SA remains unresolved. In Arabidopsis, a major part of SA is derived from isochorismate, a key intermediate produced by the isochorismate synthase, which is reminiscent of SA biosynthesis in bacteria. Whereas bacteria employ an isochorismate pyruvate lyase (IPL) that catalyzes the turnover of isochorismate to pyruvate and SA, plants do not contain an IPL ortholog and generate SA from isochorismate through an unknown mechanism. Combining genetic and biochemical approaches, we delineated the SA biosynthetic pathway downstream of isochorismate in Arabidopsis. We found that PBS3, a G H3 acyl adenylase-family enzyme important for SA accumulation, catalyzes ATP- and Mg2+-dependent conjugation of L-glutamate primarily to the 8-carboxyl of isochorismate and yields the key SA biosynthetic intermediate, isochorismoyl-glutamate A. Moreover, we discovered that EPS1, a BAHD acyltransferase-family protein with a previously implicated role in SA accumulation upon pathogen attack, harbors a noncanonical active site and an unprecedented isochorismoyl-glutamate A pyruvoylglutamate lyase activity that produces SA from the isochorismoyl-glutamate A substrate. Together, PBS3 and EPS1 form a two-step metabolic pathway to produce SA from isochorismate in Arabidopsis, which is distinct from how SA is biosynthesized in bacteria. This study closes a major knowledge gap in plant SA metabolism and would help develop new strategies for engineering disease resistance in crop plants.