Responses of the Necrotrophic Fungus to the Indolic Phytoalexin Brassinin

causes black spot disease in . During host infection, this necrotrophic fungus is exposed to various antimicrobial compounds, such as the phytoalexin brassinin which is produced by many cultivated species. To investigate the cellular mechanisms by which this compound causes toxicity and the corresponding fungal adaptive strategies, we first analyzed fungal transcriptional responses to short-term exposure to brassinin and then used additional functional approaches. This study supports the hypothesis that indolic phytoalexin primarily targets mitochondrial functions in fungal cells. Indeed, we notably observed that phytoalexin treatment of disrupted the mitochondrial membrane potential and resulted in a significant and rapid decrease in the oxygen consumption rates. Secondary effects, such as Reactive oxygen species production, changes in lipid and endoplasmic reticulum homeostasis were then found to be induced. Consequently, the fungus has to adapt its metabolism to protect itself against the toxic effects of these molecules, especially the activation of high osmolarity glycerol and cell wall integrity signaling pathways and by induction of the unfolded protein response.