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Processing and release of the maize phytocytokine Zip1

ABSTRACT: Phytocytokines are peptide signaling molecules in plant immunity. 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. C-terminal PROZIP1 translocates to the apoplast via an unconventional secretion pathway, likely involving exocyst-positive organelles (EXPO). The combination of antibody detection, protease cleavage assays and mass spectrometry provided evidence for a proteolytic cascade, in which intracellular processing of PROZIP1 is executed by the calcium-dependent metacaspases ZmMC9 through arginine-dependent cleavage. After secretion, C-terminal PROZIP is processed by apoplastic PLCPs, which release, but also degrade the Zip1 peptide. Together, these findings reveal a two-step mechanism of phytocytokine processing, translocation, activation and clearance.

ORGANISM(S): Zea mays

PROVIDER: GSE299461 | GEO | 2026/06/17

REPOSITORIES: GEO

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	GSE299461_gene_count.xls.gz	Xls
	GSE299461_gene_fpkm.xls.gz	Xls

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Project description:Background: Occludin is a key tight junction protein that contributes to epithelial barrier integrity and inflammatory regulation. Although its structural roles are well characterized, the physiological relevance of its C-terminal domain in airway inflammation remains poorly defined. Methods: Occludin expression in human lung disease tissues was examined by immunohistochemistry. Functional relevance was assessed using BEAS-2B cells overexpressing full-length occludin or C-terminal deletion mutants. A synthetic peptide derived from the occludin C-terminal core sequence was designed and evaluated for its anti-inflammatory and barrier-protective effects. In vitro assays included IL-8 secretion, transepithelial electrical resistance, cytoskeletal remodeling, mitochondrial function, ROS production, and transcriptomic profiling. Therapeutic efficacy was validated in a murine model of Pseudomonas aeruginosa LPS–induced airway inflammation, followed by cytokine analysis, histopathology, and immune profiling. Results: Occludin expression was markedly reduced in inflamed human lung tissues. In BEAS-2B cells, occludin overexpression suppressed LPS-induced IL-8 release, restored barrier integrity, and reduced F-actin remodeling, whereas C-terminal deletion abolished these effects. The C-terminal occludin peptide significantly decreased IL-8 production, improved barrier function, and suppressed cytoskeletal changes, while a mutant peptide was ineffective. Transcriptomic analyses identified occludin as a central suppressor of inflammatory signaling. Mechanistically, the peptide inhibited p38 activation, preserved mitochondrial structure, and reduced ROS production. In vivo, peptide pretreatment improved survival, lowered IL-6, IL-8, and TNF-α levels, and reduced goblet cell hyperplasia and inflammatory infiltration. Immune profiling further revealed restored T-cell populations, reduced myeloid expansion, and enhanced M2 macrophage polarization. Conclusion: The occludin C-terminal–derived peptide exerts robust anti-inflammatory and barrier-protective effects, representing a promising therapeutic candidate for LPS-induced and potentially broader inflammatory lung diseases.

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Processing and release of the maize phytocytokine Zip1

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