Arabidopsis thaliana is a host of Phytophthora capsici

The soil-borne oomycete pathogen Phytophthora capsici is able to infect a wide range of plants and causes extensive losses in Solanaceous and Cucurbitaceae crop plants. Our understanding on the interactions between P. capsici and its host plants will greatly benefit from knowledge obtained on model pathosystems. Here, we describe a novel pathosystem between P. capsici and Arabidopsis. We screened a large collection of Arabidopsis accessions with several isolates of P. capsici, and found interaction specificity among various isolate-accession combinations. In susceptible plants, appressoria-mediated infection was followed by formation of infection hyphae, haustoria, and sporangia. During the infection process, no obvious host responses except a weak accumulation of H2O2 were detected. In incompatible interactions, appressoria formation was evident, but cell penetration was rare. In the few successful occasions of cell penetration, Arabidopsis reacted with a cell death response, with strong accumulation of H2O2 and O2- at the attempted penetration sites, and P. capsici hyphal growth and sporangia formation were early ceased. The defense-related gene expression were differentially induced between compatible and incompatible interactions, and resistance to P. capsici was compromised in some defense signaling mutants impaired in accumulation of salicylic acid, camalexin and indole-glucosinolates.