Characterization of Arabidopsis thaliana INHIBITOR OF PEP ACTION (IPA), a truncated PEPR homolog
Plants rely on innate immunity to perceive pathogens and attackers at a cellular level. Once recognized, defense signaling and amplification can be accomplished though production of plant elicitor peptides (Peps) and their interaction with their receptors (PEPRs) to initiate a number of defense responses. Here, we characterize INHIBITOR OF PEP ACTION (IPA) as a negative regulator of the Pep signaling pathway in Arabidopsis. This protein was identified as apoplastic and soluble with 77% identity to PEPR1’s extracellular domain, resembling a truncated version of the Pep receptors and similar in structure to a mammalian decoy receptor. Plants overexpressing IPA showed reduced production of reactive oxygen species (ROS), while IPA-deficient plants exhibited more robust immune responses. IPA expression was also shown to be induced by AtPep1 in root tissue, but was not elicited by other microbe-associated molecular patterns (MAMPs). Suspension cells pretreated with high concentrations of AtPep1 transcribed IPA at higher levels and were desensitized to subsequent AtPep1 treatment. Competition assays utilizing transgenic Nicotiana benthamiana demonstrated that IPA was able to compete with PEPR2 for binding of AtPep1, reducing signal transduction. Taken together, this data implicates IPA as a potentially novel decoy receptor responsible for regulating innate immunity in plants.