Prosystemin: a Hub of Tomato Plant Defense Responses

Plants live in a complex environment suffering various stress constraints. To counteract stress condition plants have evolved sophisticated defense systems. In tomato plants a key role in defense is played by systemin (Sys), an octadecapeptide, released upon leaf damage from a larger precursor, prosystemin (Prosys). Considering the need to reduce the agro-chemicals we investigated foliar and hydroponic application of Sys to tomato plants that increased both direct and indirect defenses (Chapter 1): treated plants strongly reduce growth and vitality of Spodoptera littoralis larvae also damaging the development of future insect generations. In addition, Sys treated plants reduce leaves colonization of the necrotrophic fungus Botrytis cinerea and have an increased level of attractiveness of natural herbivores antagonists. In order to investigate the molecular mechanism underpinning Prosys' defence activation, a prediction study of protein-protein interactions (PPIs) was done (Chapter 2). More than 16000 interactions were captured from the interactome query and, among them, 98 Prosys direct interactors were catalogued using GO terms. Prosys sub-network evidenced that Prosys links with two large groups of kinases and transcription factors confirming that the precursor is associated with the very early steps of plant stress perception. Prosys PPIs were also investigated in vitro and in vivo (Chapter 3). Affinity Purification Mass Spectrometry (AP-MS) detected more than 300 Prosys interactors. Some PPIs were validated through BiFC. Overall, the results proved that Sys is a very effective plant protectant, and its use could reduce the application of chemical pesticide while Prosys is involved in a large number of interactions possibly due to its ID structure and consequent biological function.