Ecological costs of biotrophic versus necrotrophic pathogen resistance, the hypersensitive response and signal transduction

Recent advances along numerous research avenues show that plant interactions with biotrophic and necrotrophic pathogens use similar pathways with opposing effects. The hypersensitive response is associated with increased biotroph resistance but decreased necrotroph resistance. In plant/herbivore interactions, opposing effects of defenses against specialist versus generalist herbivores are controlled by plant secondary metabolites, where a metabolite that provides resistance to generalist herbivores may stimulate specialist herbivores. This multi-trophic interaction is presented as an ecological cost of plant resistance, but similar concepts are rarely applied to plant interactions with different classes of pathogens. In this review, we begin to describe how necrotrophic pathogens may place an ecological cost upon plant resistance to biotrophic pathogens. We separate these potential ecological costs into three concepts: (1) the local cost of the hypersensitive response, (2) organismal cost of having machinery for a hypersensitive response and (3) antagonism between salicylate and jasmonate signaling. We describe the literature supporting these concepts and some predictions that they generate.