Submitted to: Molecular Plant Microbe International Symposium
Publication Type: Abstract only
Publication Acceptance Date: 6/30/2001
Publication Date: 7/10/2001
Citation: Hirano, S.S., Willis, D.K., Upper, C.D. 2001. Integrating findings from the lab and field toward understanding the biology of pseudomonas syringae-plant interactions. Molecular Plant Microbe International Symposium. Interpretive Summary:
Technical Abstract: Intensive laboratory studies have identified a large number of genes that affect pathogenicity in Pseudomonas syringae (Ps). In such studies, pathogen-plant interactions are usually assessed by infiltration of bacteria into leaves. Although leaf infiltration assays are an appropriate first step in identifying genes that affect pathogen-plant interactions, they circumvent a large proportion of the natural interactions that occur between bacteria and plants in the field. To place pathogenicity genes in the context of the overall life strategy of Ps, we examined the dynamics of population sizes of mutants of Ps pv. syringae B728a bearing defects in genes in the hrp and gac regulons in field experiments. hrp secretion mutants were impaired in their ability to colonize leaves, but not germinating seeds. Because these mutants caused disease in the field, the role of the secretion system in pathogenicity appears to be largely mediated by its requirement for bacterial growth. Although the non-lesion forming gacS and salA mutants of B728a were indistinguishable from B728a in laboratory leaf infiltration assays, fitness of the mutants in the field were significantly different from each other and from B728a We have additionally examined the effect of the tomato speck resistance locus, Pto, on population sizes of Ps pv. tomato SM78-1 in field experiments. Interestingly, race-shift mutants of SM78-1 were isolated from Pto leaves with relatively large numbers of the marked strain. The mutants will be used to assess the effect of race change on fitness of Pst in the field.