The immediate activation of defense responses in Arabidopsis roots is not sufficient to prevent Phytophthora parasitica infection
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- •The outcome of plant–microbe interactions is determined by a fine-tuned molecular interplay between the two partners. Little is currently known about the molecular dialogue between plant roots and filamentous pathogens. We describe here a new pathosystem for the analysis of molecular mechanisms occurring during the establishment of a compatible interaction between Arabidopsis thaliana roots and a root-infecting oomycete.
- •We performed cytological and genetic analyses of root infection during the compatible interaction between A. thaliana and Phytophthora parasitica.
- •Phytophthora parasitica uses appressoria to penetrate A. thaliana roots. Initial biotrophic growth is accompanied by the formation of haustoria, and is followed by a necrotrophic lifestyle. Arabidopsis thaliana mutants with impaired salicylic acid (SA), jasmonic acid (JA) or ethylene (ET) signaling pathways are more susceptible than the wild-type to infection. The salicylate- and jasmonate-dependent signaling pathways are concertedly activated when P. parasitica penetrates the roots, but are downregulated during invasive growth, when ethylene-mediated signaling predominates.
- •Thus, defense responses in A. thaliana roots are triggered immediately on contact with P. parasitica. Our findings suggest that the pattern of early defense mechanism activation differs between roots and leaves.