Identification and characterization of effector proteins of Hyaloperonospora parasitica and their host targets in Arabidopsis thaliana

Oomycete pathogens cause devastating plant diseases worldwide, including potato late blight and sudden oak death. Little is known about the interactions between oomycetes and their host plants at the molecular level. The proposed research aims at elucidating the molecular basis for oomycete pathogenesis and host resistance utilizing the Hyaloperonospora parasitica/Arabidopsis thaliana model pathosystem. Resistance in Arabidopsis against its native oomycete pathogen H. parasitica is usually conferred by structurally conserved Resistance (R) proteins, which recognise the presence or activity of cognate effector proteins and initiate a hypersensitive response. To date, all characterized oomycete effectors contain a conserved RXLR signal sequence, which is important for delivery of the effectors to the host cytoplasm where they exert virulence function and/or are recognized by host R protein receptors. Genomic sequence data available for H. parasitica and other oomycetes enables the identification of putative effector proteins using bioinformatics approaches. During preliminary work, 149 putative effectors were identified in H. parasitica, and the characterization of their functions, cognate R proteins and/or other targets in Arabidopsis is the overall aim of this research project. Starting from a prioritized list of effectors based on homology searches, their virulence function will be investigated in infection assays using a high-throughput surrogate bacterial type three secretion system. Utilizing a large set of 95 Arabidopsis accessions in these inoculation assays will allow the investigation of natural variation in recognitional specificity, providing data useful for the identification of putative cognate R protein receptors by association mapping. Additional approaches to investigate function and targets of putative effectors will utilize transient expression assays in Nicotiana benthamiana and yeast-two-hybrid technology. Based on preliminary data this research is expected to unravel a number of novel components important in both promoting disease in oomycetes as well as in conferring resistance in plants. Knowledge gained from the proposed research will provide further insight into the molecular basis of plant-oomycete interactions that may be extrapolated into agriculturally important pathosystems such as the potato late blight pathogen Phytophtora infestans and its hosts.