1887

Abstract

and are ubiquitous insect pathogens and possible plant symbionts, as some strains are endophytic or colonize the rhizosphere. We evaluated 11 strains of and , and two soil saprophytes (the non-rhizospheric and the rhizosphere-competent ) for their ability to germinate in bean root exudates (REs). Our results showed that some generalist strains of were as good at germinating in RE as , although germination rates of the specialized acridid pathogen and the strains were significantly lower. At RE concentrations of <1 mg ml, strain ARSEF 2575 showed higher germination rates than . Microarrays showed that strain 2575 upregulated 29 genes over a 12 h period in RE. A similar number of genes (21) were downregulated. Upregulated genes were involved in carbohydrate metabolism, lipid metabolism, cofactors and vitamins, energy metabolism, proteolysis, extracellular matrix/cell wall proteins, transport proteins, DNA synthesis, the sexual cycle and stress response. However, 41.3 % of the upregulated genes were hypothetical or orphan sequences, indicating that many previously uncharacterized genes have functions related to saprophytic survival. Genes upregulated in response to RE included the subtilisin Pr1A, which is also involved in pathogenicity to insects. However, the upregulated adhesin specifically mediates adhesion to plant surfaces, demonstrating that has genes for rhizosphere competence that are induced by RE.

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2011-01-01
2024-03-28
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