The bacterial pathogen Pseudomonas syringae suppresses MAMP-triggered Ca2+ influx in a partly effector-independent manner
M. CAVDAR (1), R. Panstruga (1) (1) RWTH Aachen, Germany

During infection, the bacterial pathogen Pseudomonas syringae DC3000 (Pst DC3000) releases microbe associated molecular patterns (MAMPs), which elicit prototypical defense reactions in host plants. To overcome host innate immunity, Pst DC3000 secretes protein effectors via the type-III secretion system. One of the earliest immune responses upon the recognition of MAMPs and DAMPs (damage associated molecular patterns) by specific pattern recognition receptors (PRRs) is a dramatic Ca2+ influx from the apoplast into the cytoplasm of plant cells. The influence of the Pst DC3000 strain on this MAMP/DAMP-triggered Ca2+ influx in the model plant Arabidopsis thaliana is not well studied yet. Hydroponically grown plants inoculated with Pst DC3000 showed strong suppression of cytosolic Ca2+ influx upon subsequent (at 24 hpi and 48 hpi) stimulation with various MAMPs. In addition, MAMP-induced accumulation of ROS (reactive oxygen species) and transcript accumulation of the defence-related gene FRK1 were also strongly reduced following Pst DC3000 infection. The near-complete bacterial inhibition of MAMP-triggered Ca2+ influx was partially relieved in Pst DC3000 mutants that are defective in the delivery of type-III effector proteins. Detailed analysis on the basis of mutants in single effectors with known immune-suppressive activity (AvrPto, AvrPtoB) or deletion of entire effector clusters revealed a combinatorial contribution of type-III effectors to this phenomenon. In sum our data suggest that suppression of plant defence by Pst DC3000 relies in part on mechanisms that are independent of the type-III secretion machinery.

Abstract Number: P7-159
Session Type: Poster