Expressing yeast SAMdc gene confers broad changes in gene expression and alters fatty acid composition in tomato fruit

Abstract

Tomato (Solanum lycopersicum) fruits expressing a yeast S-adenosyl methionine decarboxylase (ySAMdc) gene under control of a ripening-induced promoter show altered phytonutrient content and broad changes in gene expression. Genome-wide transcriptional alterations in pericarp tissues of the ySAMdc-expressing fruits are shown. Consistent with the ySAMdc expression pattern from the ripening-induced promoter, very minor transcriptional alterations were detected at the mature green developmental stage. At the breaker and red stages, altered levels of numerous transcripts were observed with a general tendency toward upregulation in the transgenic fruits. Ontological analysis of up- and downregulated transcript groups revealed various affected metabolic processes, mainly carbohydrate and amino acid metabolism, and protein synthesis, which appeared to be intensified in the ripening transgenic fruits. Other functional ontological categories of altered transcripts represented signal transduction, transcription regulation, RNA processing, molecular transport and stress response, as well as metabolism of lipids, glycans, xenobiotics, energy, cofactors and vitamins. In addition, transcript levels of genes encoding structural enzymes for several biosynthetic pathways showed strong correlations to levels of specific metabolites that displayed altered levels in transgenic fruits. Increased transcript levels of fatty acid biosynthesis enzymes were accompanied by a change in the fatty acid profile of transgenic fruits, most notably increasing ω-3 fatty acids at the expense of other lipids. Thus, SAMdc is a prime target in manipulating the nutritional value of tomato fruits. Combined with analyses of selected metabolites in the overripe fruits, a model of enhanced homeostasis of the pericarp tissue in the polyamine-accumulating tomatoes is proposed.