Localized control of cell death is crucial for the resistance of plants to pathogens. Papain-like cysteine proteases (PLCPs) regulate plant defence to drive cell death and protection against biotrophic pathogens. In maize (Zea mays), PLCPs are crucial in the orchestration of salicylic acid (SA)-dependent defence signalling. Despite this central role in immunity, it remains unknown how PLCPs are activated, and which downstream signals they induce to trigger plant immunity. Here, we discover an immune signalling peptide, Z. mays immune signalling peptide 1 (Zip1), which is produced after salicylic acid (SA) treatment. In vitro studies demonstrate that PLCPs are required to release bioactive Zip1 from its propeptide precursor. Conversely, Zip1 treatment strongly elicits SA accumulation in leaves. Moreover, transcriptome analyses revealed that Zip1 and SA induce highly overlapping transcriptional changes. Consequently, Zip1 promotes the infection of the necrotrophic fungus Botrytis cinerea, while it reduces virulence of the biotrophic fungus Ustilago maydis. Thus, Zip1 represents the previously missing signal that is released by PLCPs to activate SA defence signalling.
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This work is funded by the German Research Foundation (DFG) via grant DO 1421/5-1 (GD). Mass spectrometry work was financially supported by an ERC starting grant (M.K., grant No. 258413) and the Deutsche Forschungsgemeinschaft (M.K., grant no. INST 20876/127-1 FUGG). Research in the Zipfel laboratory is supported by the Gatsby Charitable Foundation. We are very grateful to R. Kahmann for helpful discussions and the Max Planck Institute for Terrestrial Microbiology, Marburg, Germany, for continuous support and access to laboratory facilities. We are also very thankful to A. Matei for meaningful discussions and for critical reading the manuscript. We thank R. van der Hoorn (Oxford University) for generously providing us with ABPP probes.
S.Z., K.L. and G.D. designed the experiments and analysed the data. S.Z., K.L. and B.A. performed the functional analysis of Zip1/PROZIP1. N.H. and C.Z. designed and analysed ROS and MAPK assays. Y.D., A.H. and E.S. designed, performed and analysed salicylic acid measurements. U.L. analysed the transcriptome data. F.K., T.C. and M.K. performed MS experiments and MS-related data analysis. S.Z. and G.D. wrote the manuscript with input from all authors.
The authors declare no competing interests.
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Supplementary Materials and Methods, Supplementary References, Supplementary Figures 1–7, Supplementary Table 2, Supplementary Table 3.
Complete gene list of RNAseq analyses with differentially expressed genes in response to SA and Zip1 compared to mock samples, respectively
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Ziemann, S., van der Linde, K., Lahrmann, U. et al. An apoplastic peptide activates salicylic acid signalling in maize. Nature Plants 4, 172–180 (2018). https://doi.org/10.1038/s41477-018-0116-y
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