Prosystemin coordinates multiple responses in tomato.

In Solanaceae, a family of peptide hormones called Systemins are involved in the activation of defense genes in response to wounding and herbivory. In tomato, Systemin (Sys) is an 18-aa oligopeptide released from a cytosolic precursor protein of 200 aa called prosystemin (ProSys). ProSys involvement in tomato response to chewing insects has long been described, but little is known about its role in modulating defense responses to phloem-feeding insects or other biotic agents such as pathogenic fungi. The aim of this research activity is to shed more light on ProSys involvement in tomato responses against several stress conditions and to evaluate a possible use of this plant hormone as a broad-spectrum defence instrument. For this reason, tomato cv. “Red Setter” was chosen to over-express ProSys gene since this tomato cultivar lacks the dominant allel at Mi locus, a gene involved in resistance against aphids, nematodes and white flies (Rossi et al., 1998). Solanum lycopersicum cv. “Red Setter” was genetically transformed via A. tumefaciens containing the pMZ vector carrying 35S2:prosystemin, already described by Rocco and collaborators (2008). ProSys conferred-resistance to aphids and fungi was underlined by bioassays. Tomato responses were further investigated by time-course transcriptional analysis of untransformed “Red Setter” plants challenged by aphids or fungi. The comparison with the expression profiles of the same genes in ProSys over-expressing plants underlined that ProSys induces most of the genes associated to tomato responses against these pests. In order to get a global vision of ProSys impact on tomato transcriptome, a microarray analysis was carried out underlining many defence-related differentially expressed genes, most of them supporting these biological evidences. The functional analyses of differentially espressed genes indicated that prosystemin affects genes involved in JA-, SA-, ET and auxin pathways. Molecular data were further investigated in silico to predict networks that highlight protein-protein interactions active in the signaling cascade activated by ProSys gene. This work was carried out at the Bioinformatic Department of “Centro de Investigation Principe Felipe” (CIPF, Valencia). The resulted network contained 195 proteins and highlighted some possible novel interactions such as between the ProSys-regulated ERD4 (early responsive to dehydration) and FPS (pharnesyl pyrophosphate synthase), a promising molecular link between abiotic and biotic response.