A multi-repeat adhesin of the phytopathogen, Pectobacterium atrosepticum, is secreted by a Type I pathway and is subject to complex regulation involving a non-canonical diguanylate cyclase

Daniel Perez-Mendoza, Sarah J. Coulthurst, Sonia Humphris, Emma Campbell, Martin Welch, Ian K. Toth, George P. C. Salmond

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    Abstract

    Cyclic diguanylate (c-di-GMP) is a second messenger controlling many important bacterial processes. The phytopathogen Pectobacterium atrosepticum SCRI1043 (Pba1043) possesses a Type I secretion system (T1SS) essential for the secretion of a proteinaceous multi-repeat adhesin (MRP) required for binding to the host plant. The genes encoding the MRP and the T1SS are tightly linked to genes encoding several putative c-di-GMP regulatory components. We show that c-di-GMP regulates secreted MRP levels in Pba1043 through the action of two genes encoding predicted diguanylate cyclase (DGC) and phosphodiesterase proteins (ECA3270 and ECA3271). Phenotypic analyses and quantification of c-di-GMP levels demonstrated that ECA3270 and ECA3271 regulate secreted MRP levels by increasing and decreasing, respectively, the intracellular levels of c-di-GMP. Moreover, ECA3270 represents the first active DGC reported to have an alternative active-site motif from the 'canonical' GG[D/E]EF. ECA3270 has an A-site motif of SGDEF and analysis of single amino acid replacements demonstrated that the first position of this motif can tolerate functional substitution. Serine in position one of the A-site is also observed in many other DGCs. Finally, another T1SS-linked regulator (ECA3265) also plays an important role in regulating secreted MRP, with an altered localization of MRP observed in an ECA3265 mutant background. Mutants defective in these three T1SS-linked regulators exhibit a reduction in root binding and virulence, confirming that this complex, finely tuned regulation system is crucial in the interaction with host plants.

    Original languageEnglish
    Pages (from-to)719-733
    Number of pages15
    JournalMolecular Microbiology
    Volume82
    Issue number3
    DOIs
    Publication statusPublished - Nov 2011

    Keywords

    • CYCLIC-DI-GMP
    • PSEUDOMONAS-FLUORESCENS WCS365
    • CAROTOVORA SUBSP ATROSEPTICA
    • BIOFILM FORMATION
    • RESPONSE REGULATOR
    • ESCHERICHIA-COLI
    • CAULOBACTER-CRESCENTUS
    • EXTRACELLULAR-MATRIX
    • ALLOSTERIC CONTROL
    • PUTIDA-BIOFILMS

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