Plant & Animal Genomes XV Conference

January 13-17, 2007
Town & Country Convention Center
San Diego, CA

Comparative Large-Scale Analysis Of Resistance Gene Evolution

Tadeusz Wroblewski ¹ , Boris Vinatzer ³ , Katherine S Caldwell¹ , Ursula Piskurewicz ¹ , Keri A Cavanaugh¹ , Joanna Jelenska ² , Gail Teitzel ² , Leah K McHale¹ , Huaqin Xu ¹ , Alexander Kozik ¹ , Oswaldo Ochoa¹ , Luis A Williams¹ , Jean T Greenberg ² , Richard W Michelmore¹

¹  The Genome Center, University of California at Davis, Davis, CA 95616, USA

²  Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637, USA

³  Department of Plant Pathology, Virginia Polytechnic Institute and State University Blacksburg, VA 24061, USA

Plants have developed sophisticated systems to recognize many proteins secreted into the plant cell by bacterial pathogens. Recognition of these effector molecules and subsequent defense induction involve several plant proteins and is often accompanied by rapid cell death – the hypersensitive response (HR).
In order to understand the co-evolution of bacterial effectors and plant disease resistance R-genes, we are conducting parallel studies of phenotypic and genetic diversity in the reaction between bacterial pathogens and multiple crop species. We have cloned over 180 confirmed and putative Type III effectors representing nearly entire secretomes of 4 different strains of Pseudomonas syringae as well as effectors from other bacterial pathogens. Agrobacterium-mediated transient expression assays were used to test for recognition of these effector proteins in the leaves of a total of 50 cultivars and species of lettuce, tomato, pepper, cotton and Arabidopsis. Almost half of the tested effectors induced HR in at least one accession. Few effectors were recognized across all species tested. Many reactions showed intra- or inter-specific variation. Similarities in the patterns of HR across tested plant accessions implicate a common mechanism of plant recognition for several homologous but also non-homologous effectors.
In complementary studies, we are using yeast two-hybrid to identity the potential plant targets of these effectors. We are also analyzing sequence diversity in R-genes and putative target proteins from multiple plant species to test for heterogeneous rates of evolution. This will determine whether variation in pathogen recognition can be accounted for by differences occurring within R-genes or host targets.