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Discovery and characterization of a second Pseudomonas protein recognized by Pto ========================================================================
- Date/Time : Fri April 4., 2003
- Speaker : Dr. Young Jin Kim
- 고려대학교 생명과학대학
- Place : Life Science Bldg. #104
- For inquires : Professor Ildoo Hwang Dept. of Life Science
생명과학과 황일두 교수 (☎279-2291)
Resistance to bacteria speck disease in tomato is mediated by the tomato Pto kinase which recognizes strains of Pseudomonas syringae pv. tomato that express the effector protein AvrPto. AvrPto likely enters the plant cell via the Pseudomonas type III secretion system where it physically interacts with Pto kinase and activates signaling pathways leading to variety of defense responses. We have recently identified another Pseudomonas effector protein, AvrPtoB, that also interacts specifically with Pto. AvrPtoB and AvrPto are similar in several discrete regions which might define their contact points with Pto. Both proteins also appear to confer virulence of Pseudomonas when the Pto kinase is not present in plant. The AvrPtoB type III effector protein is conserved among diverse plant pathogens suggesting it plays an important but hitherto unknown role in pathogenesis. Here we report that Pseudomonas AvrPtoB suppresses plant immunity and does so by inhibiting defensive programmed cell death (PCD). AvrPtoB acts inside the plant cell and inhibits PCD initiated by disease resistance proteins and the pro-apoptotic mouse protein Bax. Using deletion mutants, we identified distinct AvrPtoB domains that are necessary for host recognition and PCD inhibition. We also discovered a suppressed host resistance activity that triggers AvrPtoB-dependent immunity only in the absence of AvrPtoB PCD inhibitory activity. These findings suggest a new model, with mechanistic and structural details, of how a type III effector protein promotes disease.