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New Phytol. 2018 May;218(3):1167-1178. doi: 10.1111/nph.14568. Epub 2017 Apr 13.

Phytaspase-mediated precursor processing and maturation of the wound hormone systemin.

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Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow, 119991, Russia.
Institute of Plant Physiology and Biotechnology, University of Hohenheim, Stuttgart, 70593, Germany.
The James Hutton Institute, Dundee, DD2 5DA, UK.
Core Facility Hohenheim, Mass Spectrometry Unit, University of Hohenheim, Stuttgart, 70593, Germany.


Peptide hormones are implicated in many important aspects of plant life and are usually synthesized as precursor proteins. In contrast to animals, data for plant peptide hormone maturation are scarce and the specificity of processing enzyme(s) is largely unknown. Here we tested a hypothesis that processing of prosystemin, a precursor of tomato (Solanum lycopersicum) wound hormone systemin, is performed by phytaspases, aspartate-specific proteases of the subtilase family. Following the purification of phytaspase from tomato leaves, two tomato phytaspase genes were identified, the cDNAs were cloned and the recombinant enzymes were obtained after transient expression in Nicotiana benthamiana. The newly identified tomato phytaspases hydrolyzed prosystemin at two aspartate residues flanking the systemin sequence. Site-directed mutagenesis of the phytaspase cleavage sites in prosystemin abrogated not only the phytaspase-mediated processing of the prohormone in vitro, but also the ability of prosystemin to trigger the systemic wound response in vivo. The data show that the prohormone prosystemin requires processing for signal biogenesis and biological activity. The identification of phytaspases as the proteases involved in prosystemin maturation provides insight into the mechanisms of wound signaling in tomato. Our data also suggest a novel role for cell death-related proteases in mediating defense signaling in plants.


peptide hormone; phytaspase; precursor processing; prosystemin; tomato (Solanum lycopersicum); wound response

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