Maintaining plant immune homeostasis in the rhizosphere microbiome

植物根际微生物群落(根际微生物群)为植物寄主提供了多种益处，包括养分吸收和病原菌保护。为了在宿主存在的情况下生存，微生物必须逃避或抑制宿主的免疫。同时，为了避免微生物泛滥，植物免疫系统必须最大限度地减少非适应微生物的生长。我的实验室研究的一个主要目标是了解植物免疫系统如何在允许有益微生物区系增殖的同时排除一些微生物。为了识别抑制植物免疫所需的细菌基因和塑造根际微生物群所需的植物基因，我们使用荧光假单胞菌和模式植物拟南芥作为一个易于处理的根际微生物组模型。荧光素系统提供了分子、遗传和生化工具来回答宿主-微生物组相互作用中的基本问题。该项目提案包括三个互补的目标，旨在研究最终影响植物微生物组免疫动态平衡的细菌和植物机制。目的1：确定根际细菌酸化是如何抑制植物免疫的。用荧光假单胞菌预处理拟南芥根部，会抑制随后受到细菌鞭毛蛋白等微生物相关分子模式(MAMP)攻击时的防御反应。通过正向遗传筛选，我们发现多种细菌酸化机制抑制植物免疫。这一目标描述了改变根际pH抑制植物免疫的机制的特征。目的：研究水杨酸信号负调控因子对植物根际微生物群落的影响。植物激素水杨酸(SA)在植物免疫中起重要作用，也影响植物的代谢和发育。SA信号的正调控因子已被证明影响根际微生物群落的结构和功能。本研究的目的是研究SA信号负调控因子在植物代谢和免疫动态平衡中的作用。目标3：确定HSM基因在根际微生物群中的作用，以确定调节根际微生物群的植物基因。我们重新筛选了一组植物HSM突变体，这些突变体最初被鉴定为激素免疫串扰受损的突变体。我们鉴定了6个HSM突变体，它们支持在诺生条件下荧光假单胞菌的水平改变。本研究的目的是研究HSM基因在根际微生物群形成中的作用。这三个互补的目标将有助于确定微生物区系及其宿主如何在免疫动态平衡中取得平衡，最终导致微生物组的建立、耐受和维持。

Plant root-associated microbial communities (the rhizosphere microbiome) provide their plant hosts with diverse benefits including nutrient uptake and pathogen protection. In order to survive in the presence of a host, microbes must evade or suppress host immunity. At the same time, in order to avoid being overrun by microbes, the plant immune system must minimize the growth of non-adapted microbes. A major goal of my lab's research is to understand how the plant immune system excludes some microbes while allowing proliferation of beneficial microbiota. To identify bacterial genes required to suppress plant immunity and plant genes required to shape the rhizosphere microbiome, we use Pseudomonas fluorescens and the model plant Arabidopsis thaliana as a tractable rhizosphere microbiome model. Arabidopsis-P. fluorescens provides a system with molecular, genetic and biochemical tools to answer basic questions in host-microbiome interactions. This project proposal includes three complementary aims to study the bacterial and plant mechanisms that ultimately affect plant microbiome immune homeostasis. Objective 1: Determine how bacterial acidification of the rhizosphere suppresses plant immunity Pre-treatment of Arabidopsis roots with P. fluorescens will suppress a defense response upon subsequent challenge with a microbe-associated molecular pattern (MAMP) such as bacterial flagellin. Through forward genetic screens, we found that multiple bacterial acidification mechanisms work to suppress plant immunity. This objective describes characterization of the mechanisms by which altering the rhizosphere pH suppresses plant immunity. Objective 2: Determine how negative regulators of Salicylic Acid signaling shape the rhizosphere microbiome The plant hormone salicylic acid (SA) plays a central role in plant immunity, and also affects plant metabolism and development. Positive regulators of SA signaling have been shown to shape the rhizosphere microbiome structure and function. This objective is focused on characterizing the role of negative regulators of SA signaling in shaping plant metabolism and immune homeostasis in plant-microbiome interactions.  Objective 3: Characterize the role of HSM genes in the rhizosphere microbiome To identify plant genes that regulate the rhizosphere microbiome, we rescreened a collection of plant "hsm" mutants, which were originally identified as mutants impaired in hormone-immunity crosstalk. We identified 6 hsm mutants that support altered levels of P. fluorescens under gnotobiotic conditions. This aim focuses on characterizing the role of hsm genes in shaping the rhizosphere microbiome. These three complementary objectives will help determine how microbiota and their host strike a balance in immune homeostasis that ultimately results in establishment, tolerance and maintenance of a microbiome.