Botrytis cinerea methyl isocitrate lyase mediates oxidative stress tolerance and programmed cell death by modulating cellular succinate levels

Fungi lack the entire animal core apoptotic machinery. Nevertheless, regulated cell death with apoptotic markers occurs in multicellular as well as in unicellular fungi and is essential for proper fungal development and stress adaptation. The discrepancy between appearance of an apoptotic-like regulated cell death (RCD) in the absence of core apoptotic machinery is further complicated by the fact that heterologous expression of animal apoptotic genes in fungi affects fungal RCD. Here we describe the role of BcMcl, a methyl isocitrate lyase from the plant pathogenic fungus Botrytis cinerea, in succinate metabolism, and the connection of succinate with stress responses and cell death. Over expression of bcmcl resulted in elevated tolerance to oxidative stress and reduced levels of RCD, which were associated with accumulation of elevated levels of succinate. Deletion of bcmcl had almost no effect on fungal development or stress sensitivity, and succinate levels were unchanged in the deletion strain. Gene expression experiments showed co-regulation of bcmcl and bcicl (isocitrate lyase); expression of the bcicl gene was enhanced in bcmcl deletion and suppressed in bcmcl over expression strains. External addition of succinate reproduced the phenotypes of the bcmcl over expression strains, including developmental defects, reduced virulence, and improved oxidative stress tolerance. Collectively, our results implicate mitochondria metabolic pathways, and in particular succinate metabolism, in regulation of fungal stress tolerance, and highlight the role of this onco-metabolite as potential mediator of fungal RCD.