Processing and release of the maize phytocytokine Zip1

Several extracellular phytocytokines and their cognate membrane-receptors have been described in various species; however, processing and release of these signals remains largely unknown. The Zea mays immune peptide 1 (Zip1) is a maize-specific phytocytokine, which is associated to the salicylic acid (SA) signaling pathway.

Zip1 resides central in its precursor PROZIP1, thus C- and N-terminal cleavage is required to release bioactive Zip1 peptide. Two maize PLCPs, CP1 and CP2, were previously shown to cleave PROZIP1 in the apoplast. We investigated the localization and processing steps of PROZIP1 leading to Zip1 release and found that PROZIP1 undergoes processing in the endoplasmic reticulum (ER) and cytoplasm, where the N‑terminal PROZIP1 domain is cleaved.