Chromsome Modification and Transcription Repression in Regulation of Systemic Acquired Resistance

系统获得性抗性(SAR)是植物体内一种持久的、广谱的免疫反应，通常是在局部病原体侵染后诱导的。SAR的诱导需要信号分子水杨酸(SA)和病程相关(PR)基因的上调，PR基因编码具有抗菌活性的蛋白质。遗传学研究表明，至少有两种诱导事件。一个涉及SA激活NPR1和通过NPR1使SNI1失活，而另一个涉及NPR1依赖的、SA依赖的诱导。最近的工作表明，SNI1可能通过改变染色体结构来抑制PR基因的表达。使用创新的NAAIRS突变方法定义了SNI1的功能结构域。在SNI1的遗传背景中，SSN突变体被鉴定为影响NPR1依赖、SA依赖的PR基因表达的突变体。SSN1(AtRad51L3)的鉴定表明，染色体结构在PR基因调控中确实起着重要作用。对8个SSN突变体的鉴定表明，这一过程涉及多种成分。为了了解染色体修饰和转录抑制如何影响系统获得性抗性，本项目将集中于以下具体目标：(1)SNI1转录抑制的机制；(2)SNI1转录抑制的调控；(3)SSN突变体的克隆和鉴定。这个项目的意义是多方面的。从植物病理学家的角度来看，这项研究将有助于更好地理解SAR，这是植物的一种主要防御机制。这种抗性的诱导性可能会降低病原菌克服抗性的选择压力，并允许产生持久的、广谱抗性的作物。从分子遗传学家的观点来看，SAR是一个迷人的信号转导过程，导致基因表达的全球协调变化。植物中转录抑制的机制知之甚少，也不知道SSN1是如何调控PR基因转录的。SSN1是一个RAD51同源基因，被认为参与DNA重组和修复。对于这个项目，已经开发了一套独特的工具来在这些研究领域做出新的发现。探索病原菌攻击过程中DNA重组和PR基因表达之间的可能联系，分别影响植物的长期生存和即刻生存，将是一项有趣的工作。最后，进化生物学家还感兴趣的是，植物如何在抵御病原体挑战的能力和将抗性成本降至最低的需要之间取得平衡。该项目还将对教育产生更广泛的影响。它将为该项目的PI、研究生和博士后(均为女性)提供必要的财政支持。SSN突变体的克隆将由本科生作为他们的自主学习项目进行。这笔赠款还将促进PI在SROP计划中担任少数族裔本科生暑期研究的导师，作为大学女性科学与工程(WISE)计划的小组成员，以及植物生理学、植物杂志和MPMI的编辑。

Systemic acquired resistance (SAR) is a long lasting, broad spectrum immune response in plants that is often induced after a local pathogen infection. Induction of SAR requires the signal molecule salicylic acid (SA) and up-regulation of pathogenesis-related (PR) genes, which encode proteins with antimicrobial activities. Genetic studies suggest that there are at least two induction events. One involves activation of NPR1 by SA and inactivation of SNI1 through NPR1 while the other involves an NPR1-independent, SA-dependent induction. Recent work has shown that SNI1 might repress PR gene expression through changes in the chromosome structure. The functional domains of SNI1 have been defined using the innovative NAAIRS mutagenesis. In the sni1 genetic background, ssn mutants were identified that affect NPR1-independent, SA-dependent expression of PR genes. The identification of SSN1 (AtRad51L3) suggests that chromosome structure indeed plays an important role in PR gene regulation. Identification of eight ssn mutants implies that there are multiple components involved in this process. To understand how chromosome modification and transcription repression affect systemic acquired resistance, this project will focus on the following specific aims: (1) Mechanism of SNI1 transcriptional repression; (2) Regulation of SNI1 transcriptional repression; and (3) Cloning and characterization of ssn mutants. The significance of this project is manifold. From a plant pathologist's point of view, this study will lead to better understanding of SAR, which is a major defense mechanism in plants. The inducible nature of this resistance may reduce the selective pressure for pathogens to overcome resistance and allow the generation of crop plants with durable, broad-spectrum resistance. From a molecular geneticist's standpoint, SAR is a fascinating signal transduction process leading to a coordinated global change in gene expression. The mechanisms of transcriptional repression are poorly understood in plants, and it is not known how SSN1, a RAD51 homolog presumed to be involved in DNA recombination and repair, regulates PR gene transcription. For this project, a unique set of tools has been developed to make new discoveries in these research areas. It will be fascinating to explore the possible link between DNA recombination and PR gene expression during pathogen challenge, which affects the long-term and immediate survival of the plant, respectively. Finally, it is also of interest to evolutionary biologists how plants balance their ability to fend off pathogen challenge and the need to minimize the cost of resistance. This project will also have a broader impact on education. It will provide the necessary financial support for the PI, graduate student and postdoctoral (all women) on this project. Cloning of ssn mutants will be carried out by undergraduate students as their independent-study projects. This grant will also facilitate the PI's role as a mentor in the SROP program for minority undergraduate summer research, as a panelist in the University Women in Science and Engineering (WISE) program, and an editor for Plant Physiology, Plant Journal and MPMI.