'Candidatus Liberibacter asiaticus' Encodes a Functional Salicylic Acid (SA) Hydroxylase That Degrades SA to Suppress Plant Defenses
'Candidatus Liberibacter asiaticus' Encodes a Functional Salicylic Acid (SA) Hydroxylase That Degrades SA to Suppress Plant Defenses
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DOI：
10.1094/mpmi-12-16-0257-r
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发表时间：
2017-08-01
影响因子：
3.5
通讯作者：
Wang, Nian
中科院分区：
文献类型：
--
作者：
Li, Jinyun;Pang, Zhiqian;Wang, Nian
来自挑剔的、韧皮部限制性的“黄龙病”物种的病原体在全世界柑橘中引起毁灭性的黄龙病（HLB），并在许多茄科作物和伞形科植物上引起疾病。然而，由于培养相应的“Ca”的困难，对其致病机制知之甚少。韧皮部杆菌属。在这里，我们报告说，柑橘HLB病原体'Ca。L. asiaticus'使用活性水杨酸羟化酶SahA降解水杨酸（SA）并抑制植物防御。纯化的SahA蛋白具有很强的降解SA及其衍生物的酶活性。在转基因烟草中过量表达SahA可消除SA积累和由非寄主病原菌感染诱导的过敏反应（HR）。通过降低SA，Ca。L. SA不仅能增强柑橘对非致病性和致病性柑橘黄单胞菌的敏感性，而且能减弱柑橘对外源SA的反应。此外，叶面喷施2，1，3-苯并噻二唑和2，6-二氯异烟酸，SA功能类似物不能被SahA降解，在抑制'Ca. L.在田间条件下，感染柑橘的亚洲虎种群增长和HLB病害进展。这项研究表明，一种或多种病原体通过降解SA来抑制植物防御，并为开发基于SA衍生物的新管理方法以控制相关植物疾病提供了线索。
Pathogens from the fastidious, phloem-restricted 'Candidatus Liberibacter' species cause the devastating Huanglongbing (HLB) disease in citrus worldwide and cause diseases on many solanaceous crops and plants in the Apiaceae family. However, little is known about the pathogenic mechanisms due to the difficulty in culturing the corresponding 'Ca. Liberibacter' species. Here, we report that the citrus HLB pathogen 'Ca. L. asiaticus' uses an active salicylate hydroxylase SahA to degrade salicylic acid (SA) and suppress plant defenses. Purified SahA protein displays strong enzymatic activity to degrade SA and its derivatives. Overexpression of SahA in transgenic tobacco plants abolishes SA accumulation and hypersensitive response (HR) induced by nonhost pathogen infection. By degrading SA, 'Ca. L. asiaticus' not only enhances the susceptibility of citrus plants to both nonpathogenic and pathogenic Xanthomonas citri but also attenuates the responses of citrus plants to exogenous SA. In addition, foliar spraying of 2,1,3-benzothiadiazole and 2,6-dichloroisonicotinic acid, SA functional analogs not degradable by SahA, displays comparable (and even better) effectiveness with SA in suppressing 'Ca. L. asiaticus' population growth and HLB disease progression in infected citrus trees under field conditions. This study demonstrates one or more pathogens suppress plant defenses by degrading SA and establish clues for developing novel SA derivatives-based management approaches to control the associated plant diseases.