Eicosapolyenoic acids: novel MAMPs with reciprocal effect on oomycete-plant defense signaling networks.

Thirty years ago arachidonic (AA; 20:4 Δ ( 5,8,11,14) ) and eicosapentaenoic (EPA; 20:5 Δ ( 5,8,11,14,17) ) acids were identified as elicitors from the late blight pathogen, Phytophthora infestans, capable of triggering the dramatic shifts in isoprenoid metabolism, defense reactions, and cell death associated with the hypersensitive response of potato to incompatible races of the pathogen. ( 1) Among plant pathogens, the capacity for eicosapolyenoic acid synthesis appears to be largely restricted to oomycetes, primitive fungi (e.g., zygomycetes and chytrids), and nematodes. AA and EPA, precursors to eicosanoids that mediate inflammatory responses and serve as critical signals for immune and central nervous system functions in mammals, continue to be compelling molecules for study in plants because of what they may reveal about lipid-based signaling and induced immunity in plant-microbe interactions and possible mechanistic parallels as conserved signaling molecules across eukaryotic kingdoms. In spite of the intriguing cross-kingdom connections in AA/EPA signaling, there has been relatively little research to resolve eicosapolyenoic acid perception and action in plants, in part because of experimental limitations of systems where these fatty acids display strong activity. However, this state of affairs may change with our recent discovery that Arabidopsis responds to AA and that plants engineered to express very low levels of eicosapolyenoic acids (EP plants) have remarkably altered phenotypes to biotic challengers.