Botrytis cinerea identifies host plants via the recognition of antifungal capsidiol to induce expression of a specific detoxification gene
The gray mold pathogen Botrytis cinerea has a broad host range, causing disease in over 400 plant species, but it is not known how this pathogen evolved this polyxenous nature. B. cinerea can metabolize a wide range of phytoalexins, including the stilbenoid, resveratrol, and the sesquiterpenoids capsidiol in tobacco, and rishitin in potato and tomato. In this study, we analyzed the metabolism of sesquiterpenoid phytoalexins by B. cinerea. Capsidiol was dehydrogenated to capsenone which was then further oxidized, while rishitin was directly oxidized to epoxy-or hydroxy-rishitins indicating that B. cinerea has separate mechanisms to detoxify structurally similar sesquiterpenoid phytoalexins. RNAseq analysis revealed that a distinct set of genes were induced in B. cinerea when treated with capsidiol or rishitin, suggesting that B. cinerea can distinguish structurally similar phytoalexins to activate appropriate detoxification mechanisms. The gene most highly upregulated by capsidiol treatment encoded a dehydrogenase, designated Bccpdh. Heterologous expression of Bccpdh in a capsidiol-sensitive plant symbiotic fungus, Epichloe festucae, resulted in an acquired tolerance of capsidiol and the ability to metabolize capsidiol to capsenone, while B. cinerea {Delta}bccpdh mutants became relatively sensitive to capsidiol. The{Delta} bccpdh mutant showed reduced virulence on the capsidiol producing Nicotiana and Capsicum species but remained fully pathogenic on potato and tomato. Homologs of Bccpdh are not found in taxonomically distant Ascomycota fungi but not in related Leotiomycete species, suggesting that B. cinerea acquired the ancestral Bccpdh by horizontal gene transfer, thereby extending the pathogenic host range of this polyxenous pathogen to capsidiol-producing plant species. Significance StatementB. cinerea can metabolize a wide range of phytoalexins, however, the extent to which phytoalexin detoxification contributes to pathogenicity is largely unknown. In this study, we have shown that B. cinerea recognizes structurally resembling sesquiterpenoid phytoalexins, rishitin and capsidiol, to activate appropriate detoxification mechanisms. We identify Bccpdh, encoding a dehydrogenase for capsidiol detoxification, which is upregulated in B. cinerea exclusively during the infection of capsidiol producing plant species, and is required to exert full virulence. Analysis of the Bccpdh locus implicates that the gene was acquired via horizontal gene transfer. This work highlights that the polyxenous plant pathogen B. cinerea can distinguish its host plants by its anti-microbial compounds, to activate appropriate mechanisms for enhanced virulence.