Control of Symbiotic Gene Expression in Sinorhizobium meliloti

描述（由申请人提供）：细菌和多细胞宿主生物如何相互识别和反应？这是健康和疾病研究中的一个基本问题。我们的项目研究了α -变形菌种Sinorhizobium meliloti与其宿主Medicago属（如苜蓿/M.苜蓿）之间的共生关系中基因表达的控制。苜蓿和木桶-草/M。truncatula)。我们的实验室在这个复杂的共生和发育过程的早期阶段率先发现了宿主-细菌信号传导。我们已经发现，细菌在共生过程中的基因表达可以遵循六种主要模式之一（即基因在何时何地开启和关闭）。在下一个项目期间，我们将确定这些阶段特异性基因的启动子，并确定在发育过程中控制表达的调控基因和蛋白质。基因表达控制的主要参与者之一是RNA聚合酶，它识别DNA并只读出（表达）某些特定的基因。在细菌中，决定表达哪些基因的关键成分是该RNA聚合酶的sigma （σ）因子。我们发现共生需要ECF（胞质外功能）σ因子：我们现在计划分析在多阶段发育过程中控制ECF σ因子的机制。细菌的强烈反应通常发生在营养剥夺的反应中；在中国根瘤菌中，它是共生中正确基因表达所必需的。我们假设这是程序化的，而不仅仅是对营养变化的反应。我们将直接检验关于严格反应如何参与分化机制的几个假设。与此同时，我们还将研究中华根菌细胞如何对细胞表面的变化做出反应：理解这一点很重要，因为细菌表面与其真核宿主的相互作用不可避免地成为两种生物相互信号和反应的舞台。

DESCRIPTION (provided by applicant): How do bacteria and multicellular host organisms recognize and respond to each other? This is a fundamental question in studies of health and disease. Our project investigates the control of gene expression in a symbiosis between the alpha-proteobacterial species Sinorhizobium meliloti and its host, genus Medicago (such as alfalfa/M. sativa and barrel-medic/M. truncatula). Our lab has previously pioneered discoveries about host-bacterial signaling during the early steps of this complex symbiotic and developmental process. We have discovered that bacterial gene expression in symbiosis can follow one of six major patterns during symbiosis (that is, when and where the genes are turned on and off). In the next project period, we will identify promoters for these stage-specific genes and will determine the regulatory genes and proteins that control expression during development. One of the major players in gene expression control is the enzyme RNA polymerase, which recognizes DNA and reads out (expresses) only certain specific genes. In bacteria, a key component that determines which genes to express is the sigma (σ) factor of this RNA polymerase. We found that ECF (extra-cytoplasmic function) σ factors are required for symbiosis: we now plan to analyze the mechanisms by which ECF σ factors are controlled in the context of a multi-stage developmental process. The bacterial stringent response usually occurs in reaction to nutrient deprivation; in Sinorhizobium, it is required for correct gene expression in symbiosis. We hypothesize this is programmed, and not merely a response to nutrient shift. We will directly test several hypotheses about how the stringent response is involved in the mechanism of differentiation. In parallel we will also look at how Sinorhizobium cells respond to alterations at the cell surface: This is important to understand because bacterial surface interactions with its eukaryotic host inevitably become an arena in which the two organisms signal and respond to each other.