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Characterization of regulatory pathways in Xylella fastidiosa: genes and phenotypes controlled by algU.

Department of Plant Pathology and Microbiology, University of California, 900 University Avenue, Riverside, CA 92521, USA.
Applied and Environmental Microbiology (Impact Factor: 3.95). 12/2007; 73(21):6748-56. DOI: 10.1128/AEM.01232-07
Source: PubMed

ABSTRACT Many virulence genes in plant bacterial pathogens are coordinately regulated by "global" regulatory genes. Conducting DNA microarray analysis of bacterial mutants of such genes, compared with the wild type, can help to refine the list of genes that may contribute to virulence in bacterial pathogens. The regulatory gene algU, with roles in stress response and regulation of the biosynthesis of the exopolysaccharide alginate in Pseudomonas aeruginosa and many other bacteria, has been extensively studied. The role of algU in Xylella fastidiosa, the cause of Pierce's disease of grapevines, was analyzed by mutation and whole-genome microarray analysis to define its involvement in aggregation, biofilm formation, and virulence. In this study, an algU::nptII mutant had reduced cell-cell aggregation, attachment, and biofilm formation and lower virulence in grapevines. Microarray analysis showed that 42 genes had significantly lower expression in the algU::nptII mutant than in the wild type. Among these are several genes that could contribute to cell aggregation and biofilm formation, as well as other physiological processes such as virulence, competition, and survival.

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    • "A relationship between biofilm formation and disease severity has also been reported. For instance, mutations in  factor 54 (RpoN) (da Silva et al. 2008) and global regulators algU and gacA (Shi et al. 2007, 2009) reduce both biofilm formation and PD progression . Therefore, one possible explanation for why the insertion mutation into the pilL gene does not eliminate disease is that the mutants still form biofilms. "
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    ABSTRACT: Xylella fastidiosa is an important phytopathogenic bacterium that causes many serious plant diseases, including Pierce's disease of grapevines. Disease manifestation by X. fastidiosa is associated with the expression of several factors, including the type IV pili that are required for twitching motility. We provide evidence that an operon, named Pil-Chp, with genes homologous to those found in chemotaxis systems, regulates twitching motility. Transposon insertion into the pilL gene of the operon resulted in loss of twitching motility (pilL is homologous to cheA genes encoding kinases). The X. fastidiosa mutant maintained the type IV pili, indicating that the disrupted pilL or downstream operon genes are involved in pili function, and not biogenesis. The mutated X. fastidiosa produced less biofilm than wild-type cells, indicating that the operon contributes to biofilm formation. Finally, in planta the mutant produced delayed and less severe disease, indicating that the Pil-Chp operon contributes to the virulence of X. fastidiosa, presumably through its role in twitching motility.
    Molecular Plant-Microbe Interactions 06/2011; 24(10):1198-206. DOI:10.1094/MPMI-10-10-0252 · 4.46 Impact Factor
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    • "Interestingly , the AlgU regulon for the plant pathogen X . fastidiosa revealed that the conserved RNA binding protein Hfq was positively regulated by AlgU ( Shi et al . , 2007 ) . The AlgU and Hfq protein sequences of P . aerugi - nosa PAO1 and X . fastidiosa share 56% and 75% identity respectively . The major physiological functions of Hfq encompass stability control of small regulatory RNAs ( sRNAs ) and mRNAs as well as positive and negative translational regulation of target mRNAs by sRNAs ( reviewed by V"
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    • "It is hypothesized that there are different steps for attachment to xylem vessels and biofilm formation (de Souza et al., 2004). Previously, we showed that mutation of the regulatory gene algU resulted in decreased attachment, decreased biofilm formation, and decreased virulence (Shi et al., 2007). Similar results were obtained here with deletion of gacA. "
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    ABSTRACT: The xylem-limited, insect-transmitted bacterium Xylella fastidiosa causes Pierce's disease in grapes through cell aggregation and vascular clogging. GacA controls various physiological processes and pathogenicity factors in many gram-negative bacteria, including biofilm formation in Pseudomonas syringae pv. tomato DC3000. Cloned gacA of X. fastidiosa was found to restore the hypersensitive response and pathogenicity in gacA mutants of P. syringae pv. tomato DC3000 and Erwinia amylovora. A gacA mutant of X. fastidiosa (DAC1984) had significantly reduced abilities to adhere to a glass surface, form biofilm, and incite disease symptoms on grapevines, compared with the parent (A05). cDNA microarray analysis identified 7 genes that were positively regulated by GacA, including xadA and hsf, predicted to encode outer membrane adhesion proteins, and 20 negatively regulated genes, including gumC and an antibacterial polypeptide toxin gene, cvaC. These results suggest that GacA of X. fastidiosa regulates many factors, which contribute to attachment and biofilm formation, as well as some physiological processes that may enhance the adaptation and tolerance of X. fastidiosa to environmental stresses and the competition within the host xylem.
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