水杨酸羟基化调控水杨酸动态平衡的分子机理研究

水杨酸（SA）是一种酚类植物激素，在植物抗病、抗逆、衰老和生长发育中起到关键作用。维持SA在植物体内的动态平衡对其正常行使生物学功能至关重要。SA羟基化是SA的重要修饰方式，被认为是植物清除体内过多SA而维持SA动态平衡的主要途径。拟南芥中存在2，3-和2，5-二羟基苯甲酸（2，3-和2，5-DHBA）两种SA羟基化产物。我们已经报道了负责生成2，3-DHBA的SA 3-羟基化酶（S3H），但是负责生成2，5-DHBA的SA 5-羟基化酶（S5H）和SA羟基化调控SA动态平衡的分子机理还不清楚。本项目前期工作利用反向遗传学鉴定了S5H酶，初步研究了S5H的生化特性和生物学功能，在此基础上将深入探究S5H的生物学功能，进一步筛选调节S5H/S3H的转录因子和互作蛋白，解析SA羟基化调控SA动态平衡的分子机理。本项目对于阐明SA代谢途径和分子调控网络具有重要的科学意义。

Salicylic acid (SA) is a key phenolic hormone which plays essential roles in plant disease resistance, stress responses, senescence and development. It is critical for plants to modulate SA homeostasis under different conditions. SA hydroxylation is an important modification and is regarded as the major detoxification pathway to maintain the SA homeostasis in plants. Two SA hydroxyl products 2, 3-and 2, 5-dihydroxybenzoic acid (2, 5-DHBA) were reported to be the major hydroxyl SA in Arabidopsis. We have previously characterized the salicylic acid 3-hydrxoylase (S3H) which can convert SA to 2, 3-DHBA in vivo and in vitro. So far, the SA 5-hydroxylase (S5H) which converts SA to another hydroxyl product 2, 5-DHBA is still unknown. In addition, the regulation network of S3H and S5H at both transcriptional and post-transcriptional levels remain elusive. In the current proposal, we will characterize the S5H enzyme by reverse genetics strategy and further investigate its biochemical properties. Taking advantage of knock-out mutant of s5h, we will compare the biological functions of S5H and S3H in plant leaf senescence and disease resistance. Moreover, we will study the regulatory mechanisms of S3H and S5H genes at both transcriptional and post-transcriptional levels. Our research ultimately contributes the elucidation of the biochemical basis of SA metabolism and the modulation mechanism of salicylic acid homeostasis by SA hydroxylation.