Complex Sensory Network Coordinating Interactions of Pseudomonas solanacearum with Host Plants

9419582谢尔青枯假单胞菌是一种土壤传播的植物病原体，可引起多种植物的致死性枯萎病，部分原因是产生一种不寻常的胞外多糖(EPS 1)和大量的胞外蛋白(EXP)。许多毒力因子的水平由复杂的感觉网络控制，其大小、组织和其他特性使其有别于原核生物中的其他因素。该网络控制着两种形态类型之间的切换，每种形态类型可能都专门用于在不同的生态位(植物和土壤)中生存，并调节EPS I(EPS)基因和其他毒力因子的转录，以响应多种环境信号。这项工作的重点是该网络的独特分子方面，以及它的一些不寻常的调控靶标的生化和生理功能。该网络独特的信号整合蛋白XpsR的生化机制正在探索中，该机制与VsrC反应调节因子结合在一起，协调EPS启动子上的转录，以响应三种不同的信号。突变和体内足迹将被用于定义启动子序列以及XpsR和/或VsrC结合和转录激活所需的条件，以了解它们之间和/或启动子的相互作用。强大的筛选方法将被用来分离相互独立地激活EPS转录的xpsR和vsrC突变等位基因，以及不起作用的xpsR等位基因。对这些突变体的DNA序列分析和鉴定将确定XpsR和VsrC的重要结构域，这些结构域相互作用，将单个信号转导系统连接到更大的网络。另一个调节EPS I产生的网络成分是vsrAD，它似乎也调节茎定殖所需的重要侧枝。另一个受网络调控的基因Tek编码一种不寻常的59 kDa的脂蛋白，它被外部加工释放出其基本的28 kDa的C末端，成为青枯病菌的主要Exp。利用抗血清和各种突变体，标记的TEK多肽的合成、加工、定位和命运正在被监测，它们的功能以及与EPS I和毒力的明显关联。RGN11也受网络调节，似乎可以防止某些环境条件对EPS I产生的抑制。通过DNA序列分析，检测RGN11突变对EPS及相关基因表达的影响，以及更详细地表征影响RGN11功能的分子和条件，正在研究RGN11的机制及其生理意义。最后，对EPS的DNA序列进行分析，以进一步了解其新的酶，它们在EPS 1的生物合成和修饰中的作用，以及它们的生理功能。对这种在植物中引起疾病的细菌的研究可以减少细菌感染对植物造成的损害。***

9419582 Schell Pseudomonas solanacearum is a soil-borne phytopathogen that causes a lethal wilting disease of diverse plants, in part due to production of an unusual exopolysaccharide (EPS 1) and numerous extracellular proteins (EXPs). Levels of many virulence factors are controlled by a complex sensory network whose size, organization, and other properties set it apart from others found in prokaryotes. The network controls switching between two morphotypes, each probably specialized for survival in different ecological niches (plant vs. soil), and also modulates transcription of genes for EPS I (eps) and other virulence factors in response to multiple environmental signals. The focus of this work is on the unique molecular aspects of the network, and on the biochemical and physiological functions of some of its unusual regulated targets. The biochemical mechanism of the network's unique signal-integrator protein, XpsR, that in conjunction with the VsrC response regulator coordinates transcription at the eps promoter in response to three different signals is being explored, mutagenesis and in vivo footprinting will be used to define promoter sequences and conditions required for binding and transcription activation by XpsR and/or VsrC to gain insight into their interactions with each other and/or the promoter. Powerful screening methods will be used to isolate mutant alleles of xpsR and vsrC that activate eps transcription independently of each other, and nonfunctional xpsR alleles. DNA sequence analysis and characterization of these mutants will identify important domains of XpsR and VsrC that interact to link individual signal transduction systems into the larger network. Another network component regulating production of EPS I is vsrAD which appears to also regulate important penes that are required for stem colonization. Another network-regulated gene, tek, encodes an unusual 59-kDa lipoprotein that is externally processed to release its basic 28-kDa C-terminus, which becomes th e major EXP of P. solanacearum. Using antiserum and various mutants synthesis, processing, localization, and fate of labelled Tek polypeptides is being monitored their function and apparent association with EPS I and virulence. rgnll is also regulated by the network and appears to prevent inhibition of EPS I production by certain environmental conditions. The mechanism of this and its physiological significance are being investigated by: DNA sequence analysis, testing the effect of rgnll mutations on expression of eps and related genes, and characterizing in more detail what molecules and conditions affect rgnll function. Finally, DNA sequence analysis of eps are being used to gain further insight into its novel enzymes, their role in biosynthesis and decoration of EPS 1, and their physiological functions. %%% Research on this bacterium that causes disease in plants could lead to a lessening of damage done to plants by bacterial infection. ***