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Genome-Wide Analysis of Gene Expression in Ralstonia solanacearum Reveals That the hrpB Gene Acts as a Regulatory Switch Controlling Multiple Virulence Pathways

September 2005 , Volume 18 , Number  9
Pages  938 - 949

Alessandra Occhialini , 1 Sébastien Cunnac , 1 Nancie Reymond , 2 Stéphane Genin , 1 and Christian Boucher 1

1Laboratoire des Interactions Plantes-Microorganismes, INRA-CNRS, UMR2594, BP 52627, 31326 Castanet tolosan Cedex, France; 2Biologie Fonctionnelle, Insectes et Interactions (BF2I), UMR INRA/INSA de Lyon, 69621 Villeurbanne, France

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Accepted 7 May 2005.

A 70-mer oligonucleotide-based DNA microarray covering 5,074 of the 5,120 predicted genes from Ralstonia so-lanacearum has been generated and used to investigate the repertoire of genes that are under the control of the transcription activator HrpB, which governs pathogenicity in this plant pathogenic bacterium. This study identified 143 hrpB up-regulated genes and 50 hrpB down-regulated genes. In addition to extending the repertoire of type III effector proteins with 26 new candidates, this work demonstrates that the hrpB regulon extends beyond type III secretion system—related functions to include a number of genes governing chemotaxy, biosynthesis or catabolism of various low-molecular-weight chemical compounds, and siderophore production and uptake. The presence of several transcripttional regulators and a cluster of genes predicted to encode the synthesis of an acyl-homoserine lactone together with the absence of a consensus hrpII box in the promoter of a significant proportion of the hrpB-regulated genes suggest that, for some genes, hrpB regulation might be indirect. Altogether, the data indicate that hrpB acts as a master regulatory gene governing a physiological swing associated with the shift from saprophytic to parasitic life.

© 2005 The American Phytopathological Society