Endogenous Peptide Signals in Arabidopsis thaliana, their receptors and their role in innate immunity

In plant innate immunity, the first line of defense against microbial pathogens is triggered by the perception of molecular signatures of the pathogens, by a highly sensitive membrane resident immune receptors. These pathogen-associated molecular patterns (PAMPs) are perceived by pattern-recognition receptors (PRRs) of the host to initiate pattern-triggered immunity (PTI). The endogenous plant signals, which are called damage-associated molecular patterns (DAMPs), are generated under different circumstances such as wounding, biotic and abiotic stresses. The DAMPs can activate the PTI and subsequently trigger the immune system in plants. These peptide signals called plant elicitor peptides (Peps) first discovered in Arabidopsis thaliana and later their orthologues were identified in different plant species. Peps are involved in immunity against diverse biotic and abiotic stresses and can fine-tune immune signaling pathways. So far, eight endogenous signals (AtPep1 to AtPep8) are discovered in the model plant A. thaliana. Recent studies revealed that the Pep members are not redundant and each of them has a specific function. AtPeps-triggered immunity is emerging as a highly complex, dynamic and a coordinated process involved in immune signaling cascades and consequently induces adequate defense responses. Therefore, it is possible to apply synthetic Peps to induce the immune system against microbial infections in plants. Here, the recent researches and progresses on Pep-triggered signaling are presented from their first discovery until now. Furthermore, the finding of their corresponding receptors AtPEPR1 and AtPEPR2 is explained in detail. Moreover, the subsequent events in the cells as the consequence of AtPeps perception are highlighted.