Plant Immunity to Necrotrophs

Plants inhabit environments crowded with infectious microbes that pose constant threats to their survival. Necrotrophic pathogens are notorious for their aggressive and wide-ranging virulence strategies that promote host cell death and acquire nutrients for growth and reproduction from dead cells. This lifestyle constitutes the axis of their pathogenesis and virulence strategies and marks contrasting immune responses to biotrophic pathogens. The diversity of virulence strategies in necrotrophic species corresponds to multifaceted host immune response mechanisms. When effective, the plant immune system disarms the infectious necrotroph of its pathogenic arsenal or attenuates its effect, restricting further ingress and disease symptom development. Simply inherited resistance traits confer protection against host-specific necrotrophs (HSNs), whereas resistance to broad host-range necrotrophs (BHNs) is complex. Components of host genetic networks, as well as the molecular and cellular processes that mediate host immune responses to necrotrophs, are being identified. In this review, recent advances in our understanding of plant immune responses to necrotrophs and comparison with responses to biotrophic pathogens are summarized, highlighting common and contrasting mechanisms.