Complex Sensory Network Coordinating Interactions of Pseudomonas solanacearum with Host Plants

点击翻译按钮获取中文摘要

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. ***