Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/23/2007
Publication Date: 4/1/2008
Citation: Munkvold, K.R., Martin, M.E., Bronstein, P., Collmer, A. 2008. A survey of the Pseudomonas syringae pv. tomato DC3000 type III secretion system effector repertoire reveals several effectors that are deleterious when expressed in Saccharomyces cerevisiae. Molecular Plant-Microbe Interactions. 21(4):490-502. Interpretive Summary: The injection of nearly 30 virulence proteins into plant cells underlies the ability of Pseudomonas syringae pv. tomato strain DC3000 to cause disease in tomato and other host plants. The search for these virulence proteins is complicated by redundancy within the repertoire and plant sensing mechanisms, which may convert virulence activities into defense responses. On the premise that some virulence target universal eukaryotic processes and that yeast lacks plant defenses responses, the DC3000 virulence proteins were expressed in yeast. Of 27 virulence proteins tested, five were found to inhibit yeast growth and two were found to cause cell death. Inactive versions of two of these proteins did not inhibit yeast growth. Furthermore, expression of four of these proteins in yeast impaired respiration. One of those proteins appeared in yeast mitochondria and was shown to cause cell death in yeast AND plants. These results support the use of yeast for the study of plant pathogen virulence proteins.
Technical Abstract: The injection of nearly 30 effector proteins by the type III secretion system underlies the ability of Pseudomonas syringae pv. tomato strain DC3000 to cause disease in tomato and other host plants. The search for effector functions is complicated by redundancy within the repertoire and by plant R-gene sentinels, which may convert effector virulence activities into a monolithic defense response. On the premise that some effectors target universal eukaryotic processes and that yeast (Saccharomyces cerevisiae) lacks R genes, the DC3000 effector repertoire was expressed in yeast. Of 27 effectors tested, HopAD1, HopAO1, HopD1, HopN1, and HopU1 were found to inhibit growth when expressed from a galactose-inducible GAL1 promoter, and HopAA1-1 and HopAM1 were found to cause cell death. Catalytic site mutations affecting the tyrosine phosphatase activity of HopAO1 and the cysteine protease activity of HopN1 prevented these effectors from inhibiting yeast growth. Expression of HopAA1-1, HopAM1, HopAD1 and HopAO1 impaired respiration in yeast, as indicated by tests with ethanol glycerol selective media. HopAA1-1 co-localized with porin to yeast mitochondria and was shown to cause cell death in yeast and plants in a domain-dependent manner. These results support the use of yeast for the study of plant pathogen effector repertoires.