Perrar, A. | bioRxiv Science

bioRxiv2025

Processing and release of the maize phytocytokine Zip1

Phytocytokines are endogenous peptides that modulate plant immunity outcomes, yet how their maturation and spatial deployment are controlled remains unclear. Here we show that the maize phytocytokine precursor PROZIP1 is controlled by a spatially separated, two-stage proteolytic pathway that mechanistically uncouples signal activation from extracellular attenuation. PROZIP1 associates with the endoplasmic reticulum and undergoes intracellular, arginine-dependent processing by type II metacaspases, generating a C-terminal PROZIP1 fragment (Ct-PROZIP1). This processing licenses PROZIP1 for export to the apoplast via an ER-Golgi-independent route. Proteomic mapping and mutational analyses identify arginine residues flanking the Zip1 peptide as critical for efficient processing and secretion. The calcium-dependent metacaspase ZmMC9 specifically processes PROZIP1, thereby efficiently generating the bioactive Ct-PROZIP1 fragment. In the apoplast, Ct-PROZIP1 is further processed by papain-like cysteine proteases and additional extracellular proteases, contributing to Zip1 turnover and signal clearance. While the free Zip1 peptide is detected at later stages, Ct-PROZIP appears to be the primary signaling entity in modulating pathogen-induced immune responses. Together, these findings demonstrate a previously unknown complexity in peptide signaling, suggesting a multilayered control of phytocytokine activity that provides spatial and temporal precision to disease modulation in maize.

plant biology↗

bioRxiv2021

A bipartite chromatophore transit peptide and N-terminal processing of protein in the Paulinella chromatophore

The cercozoan amoeba Paulinella chromatophora contains photosynthetic organelles - termed chromatophores - that evolved from a cyanobacterium [~]100 million years ago, independently from plastids in plants and algae. Despite its more recent origin, at least one third of the chromatophore proteome consists of nucleus-encoded proteins that are imported by an unknown mechanism across the chromatophore double envelope membranes. Chromatophore-targeted proteins fall into two classes. Proteins exceeding 250 amino acids carry a conserved N-terminal sequence extension, termed the chromatophore transit peptide (crTP), that is presumably involved in guiding these proteins into the chromatophore. Short imported proteins do not carry discernable targeting signals. To explore whether the import of protein is accompanied by their N-terminal processing, here we used a mass spectrometry-based approach to determine protein N-termini in Paulinella chromatophora and identified N-termini of 208 chromatophore-localized proteins. Our study revealed extensive N-terminal modifications by acetylation and proteolytic processing in both, the nucleus and chromatophore-encoded fraction of the chromatophore proteome. Mature N-termini of 37 crTP-carrying proteins were identified, of which 30 were cleaved in a common processing region. Our results imply that the crTP mediates trafficking through the Golgi, is bipartite and surprisingly only the N-terminal third ( part 1) becomes cleaved upon import, whereas the rest ( part 2) remains at the mature proteins. In contrast, short imported proteins remain largely unprocessed. Finally, this work sheds light on N-terminal processing of proteins encoded in an evolutionary-early-stage photosynthetic organelle and suggests host-derived post-translationally acting factors involved in dynamic regulation of the chromatophore-encoded chromatophore proteome. One sentence summaryProteins targeted to the evolutionary-early-stage photosynthetic organelle of Paulinella carry a bipartite N-terminal targeting sequence that is only partially removed upon protein import.

evolutionary biology↗