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-变形菌物种苜蓿中华根瘤菌和它的宿主苜蓿属（如苜蓿/苜蓿根瘤菌）之间共生关系中基因表达的控制。sativa和barrel-medic/M.蒺藜）。 我们的实验室以前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。我们已经发现，共生中的细菌基因表达可以遵循共生过程中的六种主要模式之一（即基因何时何地打开和关闭）。 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并仅读出（表达）某些特定基因。 在细菌中，决定哪些基因表达的关键成分是这种RNA聚合酶的sigma（σ）因子。 我们发现ECF（细胞质外功能）σ因子是共生所必需的：我们现在计划分析ECF σ因子在多阶段发育过程中的控制机制。 细菌的严格反应通常发生在对营养剥夺的反应中;在中华根瘤菌中，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，而不仅仅是对营养转移的反应。 我们将直接测试几个假设，严格的反应是如何参与分化的机制。 与此同时，我们还将研究中华根瘤菌细胞如何对细胞表面的改变做出反应：这一点很重要，因为细菌与其真核宿主的表面相互作用不可避免地成为两种生物相互发出信号并做出反应的竞技场。

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.