Necrotrophic fungi: live or let die

Necrotrophic fungi are pathogens that obtain nutrients from dead cells. In this chapter three major fungal necrotrophs, Sclerotinia sclerotiorum, Botrytis cinerea, and Alternaria brassicicola, are compared and contrasted. All three fungi discussed in the chapter have recently completed genome sequences. Effective pathogenesis by S. sclerotiorum requires the secretion of oxalic acid (OA). The role of OA in fungal pathogenicity was originally demonstrated using a genetic approach. In all eukaryotes examined, reactive oxygen species (ROS) are produced during normal cellular metabolism. It is now evident that low, nonlethal concentrations of ROS can function beneficially as regulatory molecules in cell-signaling pathways. Programmed cell death (PCD) is an intentional cellular suicide that is genetically based. The result of PCD is the orderly removal of unwanted, unneeded, used, or pathological cells and under normal homeostatic conditions, is of benefit to the organism. Diseases caused by B. cinerea occur in important crop plants in all temperate climate zones, both during plant cultivation and on harvested commodities, often during storage. The SNF1 kinase plays a central role in carbon catabolite repression in Saccharomyces cerevisiae. Importantly, the addition of tryptone to spores of both Δabste12 and Δabnik1 during plant inoculation resulted in a complete restoration of pathogenicity. These results might suggest the presence of a previously undescribed nutrient- or polypeptide-sensing pathway downstream of Amk1/AbSte12 signaling pathways and a putative AbNIK1 osmoregulation pathway.