RxLR and CRN effectors of the spinach downy mildew Peronospora effusa and their interacting plant proteins

The growth and production of vegetables is restricted by crop loss to infection by plant pathogens. The pathogen Peronospora effusa, or spinach downy mildew, is the major threat to spinach production and causes tremendous yield losses every year. This multicellular pathogen enters the plants through openings in the leaves and has a hairy appearance that renders infected plants unfit for consumption. Downy mildew pathogens are known to secrete proteins called effectors into the plant tissue and even the plant cells during infection. Effectors promote infection by suppressing the plant immune system and manipulation of other plant cell processes. Usually, these manipulations occur by interaction between an effector and one or multiple plant proteins. In this thesis we newly describe the genome of Pfs strain 1 and identify the genes that encode effector proteins. We then use a selection of these effectors to identify interacting plant proteins. Eight effectors and their fourteen plant interactors were further studied. The effector proteins were found to localize to the plant cell nucleus, cytoplasm, ER and punctate structures. The majority of effectors co-localized with the identified plant proteins in the same subcellular compartment. The subcellular localization of six plant interactors and two effector proteins was altered upon co-expression of the effector and interactor proteins. These results provide a first indication that the interaction between the effectors and the plant proteins may be involved in disease development. The study of effectors and their interacting plant proteins provides a great opportunity to understand the molecular interaction between plants and pathogens and to translate that knowledge to resistance breeding