|Liu, Diana -|
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: January 12, 2010
Publication Date: January 24, 2010
Citation: Kidarsa, T.A., Henkels, M.D., Liu, D., Loper, J.E. 2010. Microarray analysis and mutagenesis of the biological control agent Pseudomonas fluorescens Pf-5. 10th Japan-U.S. Seminar: Genome-Enabled Integration of Research in Plant Pathogen Systems Program Book. Technical Abstract: The biological control agent Pseudomonas fluorescens Pf-5 suppresses seedling emergence diseases caused by soilborne fungi and Oomycetes. Pf-5 produces at least ten secondary metabolites. These include hydrogen cyanide, pyrrolnitrin, pyoluteorin and 2,4-diacetylphloroglucinol, which have known functions in biological control. Other metabolites, such as the newly characterized rhizoxin analogs and the lipopeptide, orfamide A, also display antagonistic biological activity. However, mutations resulting in loss of a single secondary metabolite often have no affect on biological control. This suggests either that multiple metabolites contribute to the biological control phenotype or that unknown gene products are involved. This question is being addressed by two methods. We are introducing unmarked deletions into each of the known and putative secondary metabolite biosynthetic gene clusters in the Pf-5 genome. Mutants having single and multiple deletions are being tested in a range of bioassays to identify the contribution of specific secondary metabolites to various toxicities exhibited by wild-type Pf-5. The second approach involves microarray analysis of Pf-5 grown on pea seed surfaces to determine the expression of known secondary metabolite genes in this environment, as well as to identify other genes potentially contributing to biological control of seedling diseases. For these studies, we compared the transcriptional response of wild-type Pf-5 and derivative strains carrying a mutation in one of the regulatory genes gacA or rpoS. The gacS/gacA two-component regulatory system is required for secondary metabolite production in Pf-5 and gacS or gacA mutations lead to reduced biological control efficacy in many strains of Pseudomonas. In contrast, mutations in the sigma factor rpoS can enhance biological control of seedling diseases caused by the Oomycete Pythium ultimum. The microarray results showed differential regulation of many secondary metabolite genes and also identified other genes of potential interest in influencing the biocontrol phenotype of Pf-5.