1.3.12

ARABIDOPSIS-PHYTOPHTHORA DEFINING AND AMENABLE PATHOSYSTEM


A ROETSCHI1, A SI-AMMOUR1, F. MAUCH1 and B MAUCH-MANI1

1Department of Biology, Plant Biology, University of Fribourg, 1700 Fribourg, Switzerland

Background and objectives
Phytophthora diseases belong to the most devastating plant diseases, and are of considerable economic and environmental importance. The analysis of the molecular basis of Phytophthora diseases is hampered by the lack of an easily amenable genetic system. Our aim was to define a plant-Phytophthora pathosystem using Arabidopsis thaliana as the host.

Results and conclusions
Screening of Arabidopsis accessions with isolates of Phytophthora ssp. resulted in the identification of interactions ranging from complete susceptibility to complete resistance. Accessions susceptible to a given isolate of Phytophthora are completely colonized within a few days. Encysted zoospores germinate at the plant surface, an appressorium is formed at the junction of epidermal cells, and penetration occurs between the anticlinal walls. The pathogen develops in the intercellular space, oospores are formed inside the colonized tissues and hyphae grow out of the stomata to give rise to zoosporangia. Thus the compatible interaction shows all the characteristics of a facultative biotrophic interaction, indicating that Phytophthora is a true pathogen of Arabidopsis. In incompatible host-pathogen combinations different degrees of resistance can be observed. The plant reacts either with a hypersensitive reaction (HR) comprising one to a few cells, or the fungus is able grow to some extent into the tissue, triggering an HR which is visible macroscopically as a necrotic fleck.

Complete diallel crosses between resistant and susceptible accessions of Arabidopsis indicate that in some combinations, resistance is inherited dominantly and follows a gene-for-gene type of resistance.We will report on the phenotypical and biochemical characterization of this novel pathosystem.