Plant Defense Signaling and Responses Against Necrotrophic Fungal Pathogens

Fungal necrotrophic pathogens cause widespread crop losses and infect a variety of plants. The perception of these pathogens or their associated signals by specific receptors in plants triggers the mitogen-activated protein kinase (MAPK) cascades and activates hormone (jasmonates and ethylene)-dependent and hormone-independent signaling, which facilitates the mounting of a defense response against the invading necrotrophs. This response involves the activation of specific transcription factors that result in the production of antifungal proteins (plant defensins) or accumulation of defensive secondary metabolites (phytoalexins). The perception and communication mechanisms triggered by pathogen-associated molecular patterns and the hormones are coordinated by the MAPK signaling cascades which integrate various aspects of the multi-layered plant defense response. This review focuses on compiling distinct and overlapping roles played by various components of the plant signaling machinery in recognizing and mounting a regulated defense response against necrotrophic fungal pathogens.