ARS | Publication request: PSEUDOMONAS GENE EXPRESSION DURING GROWTH IN THE RHIZOSPHERE

Submitted to: American Phytopathology Society
Publication Type: Abstract Only
Publication Acceptance Date: July 15, 2008
Publication Date: July 26, 2008
Citation: Gonzalez, E.T., Wechter, W.P., Kluepfel, D.A. 2008. Pseudomonas gene expression during growth in the rhizosphere. Phytopathology. 98 (6 supplements):S191

Technical Abstract: The plant rhizosphere is a nutrient rich oasis for soil dwelling microbes, both benevolent and pathogenic. Perhaps one of the best-studied groups of bacteria that live in this niche are the fluorescent pseudomonads. This due to the variety of traits they display, such as secondary metabolite production and plant disease protection. To gain a comprehensive understanding of bacterial genes that mediate rhizosphere colonization, we evaluated the expression of P. putida KT2440 genes during growth in the rhizosphere of Arabidopsis thaliana using microarrays; gene expression of all 5350 open reading frames of P. putida KT2440 was evaluated 48 and 120 hours post inoculation. A total of 1.8% and 5.5% of the P. putida KT2440 genome was modulated 48 and 120 hours post inoculation, respectively. Genes annotated as hypothetical proteins with unknown function represented the majority of genes whose expression is modulated in response to growth in the rhizosphere. These genes made up 43.8% and 41.6% of the total number of modulated genes at 48 and 120 hours post inoculation, respectively. However, genes with previously identified roles in root colonization also were induced at both time points. This group includes genes involved in chemotaxis, motility, iron sequestration, and amino acid transport and biosynthesis. Thirty-two genes were induced at both 48 and 120 hours post inoculation; therefore, we hypothesize that genes in this category are important in rhizosphere colonization. To evaluate the role of these genes in general root colonization and seed adhesion, several P. putida and P. aeruginosa mutants were tested. Results from this study, as well as two other microarray-based studies of Pseudomonas gene expression, will be discussed.