Systemic Signalling in Plant Defence

Abstract

Systemic signalling involves a complex network of signal transduction and amplification that leads to the activation of defence genes and establishment of systemic resistance throughout the entire plant. On microbial invasion, pathogen‐associated molecular patterns and effectors are frequently detected and recognized by plant receptors. Localized perception at the infection site rapidly triggers a cascade of early signalling events such as ion fluxes, protein phosphorylation and production of reactive oxygen species. Subsequently, secondary signal molecules are synthesized and involved in amplification of defence signalling and the establishment of systemic acquired resistance. In addition, crosstalks often occur among various signalling pathways, which further modulate host defence in response to different types of pathogen attack. Key concepts: Local resistance to pathogen infection generally results from PAMP (pattern‐associated molecular pattern)‐triggered immunity, otherwise known as basal defence, and microbial effector‐triggered immunity. Microbial infection of local tissues often leads to systemic acquired resistance in distal tissues which provides long‐lasting broad‐spectrum resistance to a variety of pathogens. Mobile signals for systemic acquired resistance are translocated via vasculature and may include small peptides such as AtPep1, methyl salicylate, jasmonate, azelaic acid and other lipid‐derived molecules. Both local and systemic resistance involve a complex network of signal transduction which includes extensive crosstalks among reactive oxygen species (e.g. hydrogen peroxide and nitric oxide), salicylic acid, jasmonic acid, ethylene, abscisic acid, auxin and MAP kinase signalling pathways.