CeBiTec Colloquium in collaboration with SFB 613
Monday, October 5th 2009, 10:30 a.m.
G2-104, CeBiTec building
Prof. Dr. J.R. Alfano
Center for Plant Science Innovation and the Department of Plant Pathology, University of Nebraska, Lincoln, USA
Pseudomonas syringae type III effectors: Enzymatic activities, sites of action, and their ability to suppress plant innate immunity
The bacterial pathogen Pseudomonas syringae is dependent on a type III protein secretion system and the type III effector proteins (T3Es) it injects into host cells to cause disease. The enzymatic activities of T3Es and their plant targets remain largely unknown. I will discuss our progress on the DC3000 T3E HopU1, which we determined is a mono-ADP-ribosyltransferase (ADP-RT). Using ADP-RT assays coupled with mass spectrometry we identified the major HopU1 substrates in Arabidopsis thaliana extracts to be several RNA-binding proteins that possess RNA-recognition motifs (RRMs). HopU1 ADP-ribosylates an arginine residue in position 49 of the glycine-rich RNA-binding protein AtGRP7, which is within its RRM. We found that ADP-ribosylated AtGRP7 was reduced in its ability to bind RNA. Another T3E that we are currently focused on is HopG1, which localizes to plant mitochondria and when expressed transgenically result in plants that are infertile, dwarfed, and possess increased branching. HopG1 also has the ability to suppress innate immunity, which suggests that pathogens may target mitochondria as a pathogenic strategy. Finally, I will also discuss recent experiments that suggest that the majority of DC3000 type III effectors can suppress plant immunity.