Poster: Plant-pathogen interactions
Abs #
538: Infection by virulent Pseudomonas syringae alters auxin physiology in Arabidopsis thaliana
One of the strategies utilized by plant pathogens to promote tissue colonization and disease development is the alteration of normal physiological processes within the plant, for example by modulating plant hormone physiology and/or signaling. In this study we investigated the effect of infection by the virulent bacterial pathogen Pseudomonas syringae pv. tomato strain DC3000 (PstDC3000) on the auxin physiology of Arabidopsis thaliana. We observed that within 48 hours after inoculation, the free auxin (indole acetic acid, IAA) levels in PstDC3000-infected plants was significantly higher than in un-inoculated or mock-inoculated plants. Expression of several A. thaliana genes encoding IAA biosynthetic enzymes or IAA-amino acid conjugate hydrolyases was up-regulated within 24 hours after inoculation with PstDC3000 infection, indicating that the increase in free IAA is generated, at least in part, by the plant. Interestingly, induction of several of these IAA-related genes during infection was dependent on the phytotoxin coronatine, an important virulence factor of PstDC3000, suggesting that the modulation of free IAA levels within the plant may be a virulence strategy for this pathogen. Application of exogenous auxin during infection significantly increased disease symptom severity. Further, two A. thaliana auxin signaling mutants, axr1 and axr3/iaa17, exhibited a significant reduction in susceptibility to PstDC3000. Thus, full virulence of PstDC3000 on A. thaliana plants appears to require intact auxin signaling within the plant. These findings suggest that P. syringae modulates endogenous free auxin levels within the plant as a strategy to promote pathogen virulence and disease development.
