Castaldi, Valeria (2024) FROM DEFENSE TO MICROBIOME MODIFICATION: THE TALENTED ROLE OF PROSYSTEMIN AND ITS DERIVED PEPTIDES IN TOMATO PLANTS. [Tesi di dottorato]

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Abstract

Plants have evolved intricate defense strategies over millions of years to adapt to environmental changes, but the plethora of molecules involved in these processes remains underexplored. A significant area of study focuses on signaling peptides, which hold a great potential for use in crop protection as innovative biotechnological tools. Our contribution to this field of study began with Prosystemin (ProSys), the precursor of the first signaling peptide identified in plants, Systemin (Sys), discovered by Ryan in 1991 in Solanum lycopersicum. Since previous research on ProSys revealed its activities were greater than the sole Sys contribution, our work aimed to identify ProSys smallest bioactive sequences responsible for the broader roles it plays. In Chapter 1, we identified new short peptide motifs along ProSys sequence that were tested for their biological activity. Selected peptides successfully protected tomato plants against insect pests and necrotrophic fungi without direct toxicity effects, triggering defense pathways linked to jasmonic acid (JA) and oligogalacturonides (OGs). Given that plants function as holobionts, involving dynamic interactions between the host and its associated microbiome, in Chapter 2 we explored the effects of a selected Prosys-derived peptide on the tomato phyllosphere microbiome. The peptide shaped the leaf microbiome both taxonomically and functionally, with shifts resembling microbial patterns typically associated with JA-mediated stress responses. The enrichment of a targeted microbiome positioned the peptide not only as an effective resistance elicitor, but also as a potential attractant of a specific beneficial microbiota. In Chapter 3, based on the in vivo discovery of some peptide motifs predicted in Chapter 1, it was hypothesized that ProSys might undergo further proteolytic processing to release additional peptides beyond Sys. Revealing the presence of a truncated form of ProSys lacking the Sys sequence (PSDel1-178) in chloroplasts, we proposed new pathways for ProSys fate inside the plant cell. Overall, our findings provide novel understanding into ProSys multifaceted roles in plant stress responses while underlining its potential as a valuable source of new peptide-based tools for crop protection. This investigation led to an international patent registration involving the discovered ProSys peptide motifs.

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