Functional characterization ofBotrytis cinereaABC transporter geneBcatrBin response to phytoalexins produced in plants belonging to families Solanaceae, Brassicaceae and Fabaceae

Botrytis cinerea, a generalist fungal pathogen of economically important crop species, has been shown to exhibit reduced sensitivity to fungicides and plant toxins. Specifically, previous reports indicateB. cinerea’s efficacy in tolerating a wide array of phytoalexins, toxic plant metabolites that play key role in plant immune defense strategies. Previously, we have shown that a distinct set of genes was induced inB. cinereawhen treated with phytoalexins derived from different plant species such as rishitin (tomato and potato), capsidiol (tobacco and bell pepper) or resveratrol (grape and blueberry). In this study, we focused on the functional analyses ofB. cinereagenes induced by rishitin treatment.B. cinereacan metabolize rishitin to at least 4 oxidized forms. Heterologous expression of rishitin-inducedB. cinereagenes in the plant symbiotic fungus,Epichloë festucae, revealed that oxidoreductase (Bcin08g04910) and cytochrome P450 (Bcin16g01490) genes are involved in the oxidation of rishitin. BcatrB is an exporter of structurally unrelated anti-microbial compounds such as resveratrol, camalexin and fungicide fenpicionil. Expression ofBcatrBis upregulated by rishitin, but not by structurally resembling capsidiol.BcatrBknock out transformants (ΔbcatrB) showed enhanced sensitivity to rishitin, but not to capsidiol. Likewise,ΔbcatrBshowed reduced virulence on tomato fruits (which produce rishitin), but showed full virulence onNicotiana benthamiana(which mainly produces capsidiol), suggesting thatB. cinereadistinguishes phytoalexins and activates expression of appropriate transporter genes during the infection. Activation ofBcatrBpromoter was detected using P_BcatrB:GFPtransformant during theB. cinereainfection in plant tissues. Surveying of 26 plant species across 13 families revealed that theBcatrBpromoter is mainly activated during the infection of plants belonging to the Solanaceae, Fabaceae and Brassicaceae families. TheBcatrBpromoter is activated by the treatment with Fabaceae phytoalexins medicarpin and glyceollin, andΔbcatrBshowed reduced virulence on red clover, which produces medicarpin. These results suggest thatBcatrBplays a critical role in the strategy employed byB. cinereato bypass the plant innate immune responses in a wide variety of important crops belonging to the Solanaceae, Brassicaceae and Fabaceae families.