Department of Horticulture, Cornell University, Ithaca, NY 14853, USA.
Proc Natl Acad Sci U S A. 2013 Sep 3;110(36):14807-12. doi: 10.1073/pnas.1302702110. Epub 2013 Aug 19.
The plant hormone salicylic acid (SA) plays critical roles in plant defense, stress responses, and senescence. Although SA biosynthesis is well understood, the pathways by which SA is catabolized remain elusive. Here we report the identification and characterization of an SA 3-hydroxylase (S3H) involved in SA catabolism during leaf senescence. S3H is associated with senescence and is inducible by SA and is thus a key part of a negative feedback regulation system of SA levels during senescence. The enzyme converts SA (with a Km of 58.29 µM) to both 2,3-dihydroxybenzoic acid (2,3-DHBA) and 2,5-DHBA in vitro but only 2,3-DHBA in vivo. The s3h knockout mutants fail to produce 2,3-DHBA sugar conjugates, accumulate very high levels of SA and its sugar conjugates, and exhibit a precocious senescence phenotype. Conversely, the gain-of-function lines contain high levels of 2,3-DHBA sugar conjugates and extremely low levels of SA and its sugar conjugates and display a significantly extended leaf longevity. This research reveals an elegant SA catabolic mechanism by which plants regulate SA levels by converting it to 2,3-DHBA to prevent SA overaccumulation. The research also provides strong molecular genetic evidence for an important role of SA in regulating the onset and rate of leaf senescence.
植物激素水杨酸（SA）在植物防御、应激反应和衰老中起着关键作用。尽管 SA 的生物合成已经得到很好的理解，但 SA 被分解代谢的途径仍然难以捉摸。在这里，我们报告了一种参与叶片衰老过程中 SA 分解代谢的 SA 3-羟化酶（S3H）的鉴定和特征。S3H 与衰老有关，可被 SA 诱导，因此是衰老过程中 SA 水平负反馈调节系统的关键组成部分。该酶在体外将 SA（Km 为 58.29 µM）转化为 2,3-二羟基苯甲酸（2,3-DHBA）和 2,5-DHBA，但在体内仅转化为 2,3-DHBA。s3h 敲除突变体无法产生 2,3-DHBA 糖缀合物，积累非常高水平的 SA 和其糖缀合物，并表现出早熟衰老表型。相反，功能获得系含有高水平的 2,3-DHBA 糖缀合物和极低水平的 SA 和其糖缀合物，并表现出明显延长的叶片寿命。这项研究揭示了一种优雅的 SA 分解代谢机制，植物通过将其转化为 2,3-DHBA 来调节 SA 水平，以防止 SA 过度积累。该研究还为 SA 在调节叶片衰老开始和速度方面的重要作用提供了强有力的分子遗传证据。
