Villamil, J. C. M. | Search bioRxiv

bioRxiv2026

Prion-like domains control plastid targeting of PEPSI effectors and PEPSI6-mediated modulation of DXR during root symbiosis

Microbial effectors often act in the apoplast or cytosol, but how they reach host organelles during beneficial plant-fungal interactions remains poorly understood. Here, we identify a class of secreted prion-like effector proteins from the mutualistic root endophyte Serendipita indica, termed PEPSIs. These proteins contain prion-like domains (PrLDs) embedded within intrinsically disordered regions, and three tested PEPSIs require these domains for plastid localization. Focusing on PEPSI6, we show that plastid targeting depends on its PrLD and is associated with engagement of plastid import and proteostasis machinery. In plastids, PEPSI6 associates with 1-deoxy-D-xylulose 5-phosphate reductoisomerase (DXR), promotes DXR accumulation, alters methylerythritol phosphate pathway metabolites, and enhances tolerance to the DXR inhibitor fosmidomycin. PEPSI6 also undergoes apoplastic C-terminal CAP-domain processing, and its colonization-promoting activity persists after PrLD deletion, indicating a plastid-targeting-independent function. Overall, this work identifies PrLDs as noncanonical plastid-targeting elements in PEPSI effectors and reveals DXR as a target of fungal manipulation during root symbiosis. HighlightsO_LIPrion-like domains control plastid targeting of selected PEPSI effectors. C_LIO_LIPEPSI6 associates with DXR and promotes its accumulation in plastids. C_LIO_LIPEPSI6 alters MEP-pathway metabolites and increases tolerance to fosmidomycin. C_LIO_LIApoplastic processing reveals a plastid-independent PEPSI6 activity during root symbiosis. C_LI

plant biology↗

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↗