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

病原体引起的植物病害对全球粮食安全构成重大威胁。更深入地了解植物病原体是如何引起疾病的，为制定有效的战略以控制植物疾病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，都依赖它们输送到植物细胞中的效应物来抑制植物防御和建立感染。植物激素水杨酸在植物抵御病原菌侵染中起着至关重要的作用。研究人员发现，一种III型细菌效应器针对水杨酸介导的植物防御的主调节器进行降解，从而导致疾病。本项目旨在阐明细菌效应器介导的主调控子降解的分子机制和生物学后果，并鉴定不能被效应器降解的调控子的突变形式。这种不可降解的调节剂可能被用来培育抗病植物。抗病作物对于用不断减少的耕地养活全球人口和减少对环境有害的杀虫剂的数量至关重要。每年将通过该项目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，在柑橘树在SCienceLab出现明显症状之前检测柑橘绿化病。通过将实践中的尖端实验与现实生活中迫切的植物病理学问题联系起来，这个项目将激励学生，让他们意识到植物科学的重要性。本项目的重点是通过Psudomonas syringae III型效应器AvrPtoB靶向SA激活的NPR1。虽然已知NPR1在植物局部和系统防御中发挥重要作用，但尚未有针对NPR1的病原菌效应物的报道。SA促进植物胞质内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发挥作用。该项目表明SA促进了AvrPtoB和NPR1之间的相互作用，这表明AvrPtoB只与NPR1的活性形式相互作用。本项目证明了AvrPtoB以NPR1为靶点进行降解，这取决于AvrPtoB的E3连接酶活性。此外，该项目还发现SA信号的主要调节者NPR1在MAMP触发的免疫(MTI)中起着重要作用。本建议旨在1)通过确定AvrPtoB是否只针对单体NPR1蛋白来研究SA如何促进NPR1与AvrPtoB之间的相互作用，2)确定AvrPtoB介导的多泛素化和NPR1降解的分子机制，3)展示NPR1如何对MTI做出贡献，以及4)确定AvrPtoB如何针对SA激活的NPR1来破坏依赖NPR1的MTI来破坏植物的先天性免疫。这些研究将为效应器生物学提供新的见解，并增加我们对MTI以及NPR1和SA在植物防御中的分子和生物学功能的理解。这项工作将包括培训两名博士后研究员，对来自代表性不足群体的本科生进行研究和指导，以增强他们在科学学科中追求职业生涯的能力。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.