Targeting of salicylic acid-activated NPR1 by a bacterial type III effector

由病原体引起的植物病害对全球粮食安全构成重大威胁。深入了解植物病原体如何引起疾病，为制定有效的策略来控制植物病害以实现可持续农业奠定了基础。许多植物病原体，包括真菌、细菌、线虫、细菌和卵菌，都依赖于它们传递到植物细胞中的效应物来抑制植物的防御并建立感染。植物激素水杨酸在植物抵御病原菌侵染中起着重要作用。研究人员发现，细菌III型效应物针对水杨酸介导的植物防御降解的主要调节因子，导致疾病。本项目旨在阐明细菌效应介导的主调节剂降解的分子机制和生物学后果，并鉴定一种不能被效应物降解的调节剂突变形式。这种不可降解的调节剂有可能用于培育抗病植物。抗病作物对于在日益减少的可耕地上养活全球人口以及减少对环境有害的农药的数量至关重要。每年将资助两名研究生和四名本科生。资金还将用于培训南卡罗来纳州的中学教师和学生，以便在SCienceLab的柑橘树出现明显症状之前检测出柑橘绿色病。通过将动手的尖端实验与现实生活中紧迫的植物病理学问题联系起来，该项目将激发学生并使他们意识到植物科学的重要性。本项目主要研究丁香假单胞菌III型效应物AvrPtoB对sa激活的NPR1的靶向作用。尽管多年来人们已经知道NPR1在局部和系统植物防御中起重要作用，但尚未报道病原体效应物靶向NPR1。SA促进植物胞质NPR1低聚物还原为单体，进入细胞核，作为植物防御基因的转录共激活因子。本项目表明，SA促进了AvrPtoB与NPR1的相互作用，表明AvrPtoB仅与NPR1的活性形式相互作用。该项目表明，AvrPtoB靶向NPR1降解，依赖于AvrPtoB的E3连接酶活性。此外，本项目还发现SA信号的主调控因子NPR1在MTI （MAMP-triggered immunity）中发挥重要作用。本研究旨在1)通过确定AvrPtoB是否仅靶向NPR1单体蛋白来研究SA如何促进NPR1与AvrPtoB之间的相互作用；2)确定AvrPtoB介导的NPR1多泛素化和降解的分子机制；3)揭示NPR1如何参与MTI； 4)确定AvrPtoB如何靶向SA激活的NPR1，破坏NPR1依赖的MTI，从而破坏植物先天免疫。这些研究将为效应生物学提供新的见解，增加我们对MTI以及NPR1和SA在植物防御中的分子生物学功能的认识。这项工作将包括培训两名博士后进行研究，并指导来自代表性不足群体的本科生，使他们能够从事科学学科的职业。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Plant diseases caused by pathogens pose a major threat to food security worldwide. A deeper understanding of how plant pathogens cause diseases lays foundations for developing effective strategies to keep plant diseases under control for sustainable agriculture. Many plant pathogens including fungi, bacteria, nematodes, bacteria, and oomycetes rely on effectors that they deliver into plant cells to suppress plant defenses and establish infection. The plant hormone salicylic acid plays an essential role in plant defense against pathogen infection. The investigators discovered that a bacterial type III effector targets the master regulator of salicylic acid-mediated plant defense for degradation, causing disease. This project aims to elucidate the molecular mechanism and biological consequences of the bacterial effector-mediated degradation of the master regulator, and identify a mutant form of the regulator, which cannot be degraded by the effector. This non-degradable regulator could potentially be used to generate disease-resistant plants. Disease-resistant crops are critical to feed a global world population on a decreasing amount of arable land, and to reduce the amount of environmentally harmful pesticides. Two graduate and four undergraduate students will be supported through this project each year. Funding will also be used to train middle school teachers and students in South Carolina to detect citrus greening disease before citrus trees show obvious symptoms in SCienceLab. By connecting hands-on cutting-edge experimentation with urgent real life plant pathology problems, this project will inspire students and make them aware of the importance of plant science. This project focuses on the targeting of SA-activated NPR1 by the Psudomonas syringae type III effector AvrPtoB. Though it has been known for many years that NPR1 plays an essential role in both local and systemic plant defense, it has not been reported that a pathogen effector targets NPR1. SA facilitates the reduction of plant cytosolic NPR1 oligomers into monomers, which enter the nucleus and function as transcriptional coactivators of plant defense genes. This project showed that SA promotes the interaction between AvrPtoB and NPR1, suggesting that AvrPtoB only interacts with the active form of NPR1. This project demonstrated that AvrPtoB targets NPR1 for degradation, dependent on AvrPtoB's E3 ligase activity. In addition, this project found that the master regulator of SA signaling, NPR1, plays an important role in MTI (MAMP-triggered immunity). This proposal seeks to 1) investigate how SA promotes the interaction between NPR1 and AvrPtoB by determining if AvrPtoB only targets monomeric NPR1 protein, 2) determine the molecular mechanism of AvrPtoB-mediated poly-ubiquitination and degradation of NPR1, 3) show how NPR1 contributes to MTI, and 4) determine how AvrPtoB targets SA-activated NPR1 to disrupt NPR1-dependent MTI to subvert plant innate immunity. These studies will provide fresh insights into effector biology and increase our understanding of MTI and the molecular and biological functions of NPR1 and SA in plant defense. The work will involve training of two postdoctoral fellows to perform research and mentoring of undergraduate students from under-represented groups to empower them to pursue careers in scientific disciplines.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.