Poster: Plant Pathogen/Symbiont Interactions

Abs # 692: Characterization of effector proteins from Pseudomonas

Presenter:	Morales, Christina Q., cmorales@uclink.berkeley.edu
Authors	Morales, Christina Q. (A)   Staskawicz, Brian J (A)
Affiliations:	(A): University of California, Berkeley

Pseudomonas syringae pv. tomato (Pst) DC3000 is a Gram-negative bacterial plant pathogen that causes disease on tomato and Arabidopsis. Pst DC3000 uses a type III secretion system to deliver effector proteins into the host cell to cause disease. We are studying the role of effector proteins in virulence, since it is poorly understood how effector proteins contribute to disease. Using a bioinformatics approach, we identified approximately 150 putative effectors that searched for HrpL-regulated promoter elements immediately upstream from open-reading frames. Eight putative effectors had homology to known effectors in other pathogens and were selected for further study. These homologs include avrPpiC2, avrPpiB1 (2 copies), and avrRps4 (2 copies) from Pseudomonas syringae pv. pisi, avrPphD (2 copies) from Pseudomonas syringae pv. phaseolicola, and avrXv3 from Xanthomonas campestris pv. vesicatoria. Currently, we want to determine if each effector is secreted out of the bacteria, if each effector is translocated into the plant cell, and if each effector has an effect on virulence. All effector homologs were shown to be secreted out of the bacteria. We found that avrPpiC2_DC, avrPpiB1_DC-A, avrPpiB1_DC-B, avrPphD_DC-A, avrPphD_DC-B, and avrRps4_DC-A were translocated into the plant cell using an adenylate cyclase-fusion reporter strategy. Two effectors, avrRps4_DC-B and avrXv3_DC, are required for optimum bacterial growth inside the plant cell. In addition, avrRps4_DC-B and avrXv3_DC did not appear to be translocated into plant cells. However, genetic knockouts of avrRps4_DC-B and avrXv3_DC were still able to secrete and translocate other effector proteins. Experiments to further characterize the role of avrRps4 DC-B and avrXv3_DC in virulence are in progress.