ABSTRACT
Hyaloperonospora arabidopsidis, a downy mildew pathogen of the model plant Arabidopsis, has been very useful in the understanding of the relationship between oomycetes and their host plants. This naturally coevolving pathosystem contains an amazing level of genetic diversity in host resistance and pathogen avirulence proteins. Oomycete effectors identified to date contain a targeting motif, RXLR, enabling effector entry into the host cell. The availability of the H. arabidopsidis genome sequence has enabled bioinformatic analyses to identify at least 130 RXLR effectors, potentially used to quell the host's defense mechanism and manipulate other host cellular processes. Currently, these effectors are being used to reveal their targets in the host cell. Eventually this will result in an understanding of the mechanisms used by a pathogen to sustain a biotrophic relationship with a plant.
