Maize phytocytokines and microbial-patterns trigger antagonistic features in co-incidence with wounding and fungal pathogens

Phytocytokines are signalling peptides that activate immune responses and alarm bystander cells of danger. The pathways of phytocytokine perception and activation are thought to be shared between exogenous danger signals such as microbe-associated molecular patterns (MAMPs) and endogenous, passively released, damage-associated molecular patterns (DAMPs). However, downstream responses triggered by danger molecules and their effect in plant survival is still largely unknown. Here, we have identified three biologically active maize orthologues of phytocytokines previously described in other plants. The maize phytocytokines show common features with MAMPs, including the induction of immune related genes and activation of papain-like cysteine proteases. In contrast to MAMPs, the phytocytokines do not promote cell death in the presence of wounding. In infection assays with fungal pathogens of two different life styles we found that phytocytokines affect the development of disease symptoms, likely due to the activation of phytohormonal pathways. Collectively, our results show that phytocytokines and MAMPs trigger unique and antagonistic features of immunity. We propose a model in which phytocytokines activate immune responses partially similar to MAMPs but in contrast to microbial signals, they act as danger and survival molecules to the surrounding cells. Future studies will focus on the components determining the divergence of signalling outputs upon phytocytokine activation.