S5H/DMR6 Encodes a Salicylic Acid 5-Hydroxylase That Fine-Tunes Salicylic Acid Homeostasis
S5H/DMR6 Encodes a Salicylic Acid 5-Hydroxylase That Fine-Tunes Salicylic Acid Homeostasis
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S5H/DMR6 编码水杨酸 5-羟化酶，可微调水杨酸稳态
DOI：
10.1104/pp.17.00695
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发表时间：
2017-11-01
期刊：
影响因子：
7.4
通讯作者：
Zhang, Kewei
中科院分区：
文献类型：
--
作者：
Zhang, Yanjun;Zhao, Li;Zhang, Kewei
植物激素水杨酸（SA）在生物和非生物反应、植物发育和叶片衰老中起着重要作用。2，5-二羟基苯甲酸（2，5-DHBA或龙胆酸）是绿色植物中最常见的芳香酸之一，被认为是由SA产生的，但其产生所涉及的酶仍然不清楚。DMR 6（Downy Mildew Resistant 6; At 5g 24530）已被证明在拟南芥（Arabidopsis thaliana）的植物免疫中是必不可少的，但其生化特性还不清楚。在这里，我们报告了DMR 6作为水杨酸5-羟化酶（S5 H）的发现和功能表征，该酶通过在拟南芥苯环的C5位置上羟基化SA来催化2，5-DHBA的形成。S5 H/DMR 6在体外特异性地将SA转化为2，5-DHBA，并显示出比先前报道的S3 H（K-cat/K-m = 6.09 x 10（3）M-1 s（-1））更高的催化效率（K-cat/K-m = 4.96 x 3 10（4）M-1 s（-1））。有趣的是，S5 H/DMR 6显示出底物抑制特性，可以自动控制其酶活性。S5 h突变体和S5 hs 3 h双突变体过度积累SA和显示表型，如较小的生长尺寸，早衰，和对番茄DC 3000假单胞菌的敏感性损失。S5 H/DMR 6敏感地被SA/病原体处理诱导，并且从幼苗到衰老植物广泛表达，而S3 H更特异地在成熟和衰老阶段表达。总的来说，我们的研究结果揭示了2，5-DHBA形成所需的酶的身份，并揭示了植物通过介导SA 5-羟基化来微调SA稳态的机制。
The phytohormone salicylic acid (SA) plays essential roles in biotic and abiotic responses, plant development, and leaf senescence. 2,5-Dihydroxybenzoic acid (2,5-DHBA or gentisic acid) is one of the most commonly occurring aromatic acids in green plants and is assumed to be generated from SA, but the enzymes involved in its production remain obscure. DMR6 (Downy Mildew Resistant6; At5g24530) has been proven essential in plant immunity of Arabidopsis (Arabidopsis thaliana), but its biochemical properties are not well understood. Here, we report the discovery and functional characterization of DMR6 as a salicylic acid 5-hydroxylase (S5H) that catalyzes the formation of 2,5-DHBA by hydroxylating SA at the C5 position of its phenyl ring in Arabidopsis. S5H/DMR6 specifically converts SA to 2,5-DHBA in vitro and displays higher catalytic efficiency (K-cat/K-m = 4.96 x 3 10(4) M-1 s(-1)) than the previously reported S3H (K-cat/K-m = 6.09 x 10(3) M-1 s(-1)) for SA. Interestingly, S5H/DMR6 displays a substrate inhibition property that may enable automatic control of its enzyme activities. The s5h mutant and s5hs3h double mutant overaccumulate SA and display phenotypes such as a smaller growth size, early senescence, and a loss of susceptibility to Pseudomonas syringae pv tomato DC3000. S5H/DMR6 is sensitively induced by SA/pathogen treatment and is expressed widely from young seedlings to senescing plants, whereas S3H is more specifically expressed at the mature and senescing stages. Collectively, our results disclose the identity of the enzyme required for 2,5-DHBA formation and reveal a mechanism by which plants fine-tune SA homeostasis by mediating SA 5-hydroxylation.