Institute of Biology, Leiden University, P.O. Box 9505, 2300 RA, Leiden, The Netherlands.
Mol Genet Genomics. 2018 Oct;293(5):1181-1190. doi: 10.1007/s00438-018-1450-5. Epub 2018 May 23.
Salicylic acid (SA) is an essential hormone for development and induced defense against biotrophic pathogens in plants. The formation of SA mainly derives from chorismate via demonstrated isochorismate synthase (ICS) and presumed isochorismate pyruvate lyase (IPL)-mediated steps in Arabidopsis thaliana, but so far no plant enzyme displaying IPL activity has been identified. Here, we developed an E. coli SA biosensor to screen for IPL activity based on the SalR regulator/salA promoter combination from Acinetobacter sp ADP1, to control the expression of the reporter luxCDABE. The biosensor was responsive to micromolar concentrations of exogenous SA, and to endogenous SA produced after transformation with a plasmid permitting IPTG-inducible expression of bacterial IPL in this biosensor strain. After screening a cDNA library constructed from turnip crinkle virus (TCV)-infected Arabidopsis ecotype Di-17, we identified an enzyme, PRXR1, as a putative IPL that converts isochorismate into SA. Our results provide a new experimental approach to identify IPL and new insights into the SA biosynthesis pathway in Arabidopsis.
水杨酸（SA）是植物发育和诱导防御生物营养病原体所必需的激素。在拟南芥中，SA 的形成主要来源于分支酸，通过已证实的分支酸合酶（ICS）和假定的分支酸丙酮酸裂解酶（IPL）介导的步骤，但迄今为止尚未鉴定出具有 IPL 活性的植物酶。在这里，我们开发了一种大肠杆菌 SA 生物传感器，基于不动杆菌 ADP1 的 SalR 调节剂/salA 启动子组合，通过 IPTG 诱导表达细菌 IPL 的质粒转化后，根据该生物传感器株系中内源性 SA 的产生情况，筛选 IPL 活性。该生物传感器对外源 SA 的微摩尔浓度有反应，并且对转化后产生的内源性 SA 有反应，该转化允许 IPTG 诱导表达细菌 IPL。在用芜菁黄花叶病毒（TCV）感染拟南芥生态型 Di-17 构建的 cDNA 文库筛选后，我们鉴定出一种酶，PRXR1，作为一种潜在的 IPL，将分支酸转化为 SA。我们的结果为鉴定 IPL 提供了一种新的实验方法，并为拟南芥中 SA 生物合成途径提供了新的见解。
