Chromsome Modification and Transcription Repression in Regulation of Systemic Acquired Resistance

系统获得性抗性（systemic acquired resistance，SAR）是植物在受到病原菌侵染后产生的一种广谱、持久的免疫反应。 SAR的诱导需要信号分子水杨酸（SA）和致病相关（PR）基因的上调，这些基因编码具有抗菌活性的蛋白质。遗传学研究表明，至少有两个诱导事件。一个涉及通过SA激活NPR 1和通过NPR 1灭活SNI 1，而另一个涉及NPR 1独立的SA依赖性诱导。 最近的研究表明，SNI 1可能通过改变染色体结构来抑制PR基因的表达。 SNI 1的功能结构域已被定义使用创新的NAAIRS诱变。在sni 1遗传背景中，发现了ssn突变体，它们影响PR基因的NPR 1非依赖性、SA依赖性表达。SSN 1（AtRad 51 L3）的鉴定表明染色体结构确实在PR基因调控中起重要作用。八个ssn突变体的鉴定意味着有多个组件参与这一过程。 为了了解染色体修饰和转录抑制如何影响系统获得抗性，本项目将集中在以下具体目标：（1）SNI 1转录抑制的机制;（2）SNI 1转录抑制的调控;（3）ssn突变体的克隆和表征。 这个项目的意义是多方面的。从植物病理学家的角度来看，这项研究将导致更好地了解SAR，这是一个主要的防御机制在植物。这种抗性的诱导性质可以减少病原体克服抗性的选择压力，并允许产生具有持久广谱抗性的作物植物。从分子遗传学家的角度来看，SAR是一个迷人的信号转导过程，导致基因表达的协调全球变化。转录抑制的机制在植物中知之甚少，也不知道SSN 1，一个推测参与DNA重组和修复的RAD 51同源物，如何调节PR基因转录。在这个项目中，开发了一套独特的工具，以在这些研究领域取得新的发现。探索病原菌侵染过程中DNA重组和PR基因表达之间的可能联系将是非常有趣的，它们分别影响植物的长期和即时存活。最后，进化生物学家也感兴趣的是，植物如何平衡抵御病原体挑战的能力和最小化抗性成本的需要。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独立研究项目进行。这笔赠款还将促进PI作为少数民族本科生暑期研究SROP计划的导师，作为大学妇女科学与工程（WISE）计划的导师，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.