The interaction of natural variation in a necrotrophic fungal pathogen, Botrytis cinerea, with plant defense in the Arabidopsis thaliana model system

Botrytis cinerea is an agriculturally and economically important pathogenic fungus, known to infect over 200 host plants, including the model plant Arabidopsis thaliana. Described resistance to this pathogen is quantitative and largely mediated by production of structural and chemical defenses associated with jasmonate signaling. The parameters limiting the host range of B. cinerea are ill-defined, but genetic evidence shows that B. cinerea possesses high levels of intraspecific variation and recombination. The impact of this pathogen variation on plant defense is unknown.;This research combines population, quantitative, and molecular genetics to investigate naturally variable molecular mechanisms controlling Arabidopsis---Botrytis interactions. Description of intraspecific diversity of pathogenesis-enhancing polygalacturonases produced by B. cinerea enabled informed selection from available isolate diversity for use in plant interaction studies. Virulence-associated polygalacturonases showed increased levels of amino acid sequence variation relative to reference loci, but this variation was not structured by host or geographic origins. Natural variation among Arabidopsis accessions identified quantitative trait loci (QTL) controlling plant resistance to diverse B. cinerea isolates. While genetic control of A. thaliana resistance to B. cinerea proved complex, involving numerous multi-locus interactions, QTL identified by the four B. cinerea isolates tested were surprisingly consistent, providing promising material for development of broad resistance. In contrast, testing A. thaliana mutants with genetic lesions in the jasmonate signaling pathway revealed cryptic B. cinerea variation for activation of host defenses. B. cinerea isolates varied in their induction of the phytoalexin camalexin in the absence of functional jasmonate signaling. Continuing exploration of the basis of this cryptic variation in pathogenesis suggests the involvement of several previously-undescribed plant molecular pathways in signaling defense against B. cinerea. While ignoring the diversity of B. cinerea can create confusion regarding plant interactions with this pathogen, characterized diversity can serve as a tool for identifying novel components of the interaction and development of plant resistance.