Polyamines as anabolic growth regulators revealed by transcriptome analysis and metabolite profiles of tomato fruits engineered to accumulate spermidine and spermine

Transgenic tomato (Solanum lycopersicum) genotypes that were engineered to contain high endogenous polyamines levels in fruit due to a ripening targeted expression of yeast SAM decarboxylase were used as a model system to determine the effects of enhanced spermidine (Spd) and spermine (Spm) on gene expression. Subtractive cloning of total RNA of transgenic from wild type ripening fruits resulted in isolation of several genes that were up-regulated and represented a wide range of functional classifications. To establish the global pattern of gene expression in transgenic and wild-type fruit, a custom array containing 1066 unique fruit cDNA was constructed and used to quantify levels of a large number of transcripts in transgenic and wild-type fruits during the ripening. About one-quarter of genes on the array were differentially regulated in transgenic compared to wild type fruits. The differentially up-regulated genes were twice as abundant as down-regulated genes in the high polyamine fruits. The differentially expressed genes represented functional categories including transcription, translation, signal transduction, chaperone family, stress related, amino acid biosynthesis, ethylene biosynthesis and action, polyamine biosynthesis, isoprenoid pathway, and flavonoid biosynthesis. About 44% of the differentially regulated cDNAs included genes encoding products not yet classified for the functional attributes. Based on the results presented here on the limited transcriptome in conjunction with metabolite profiles showing significant enhancement of anabolic pathways in transgenic fruits, we propose that Spd/Spm act as anabolic growth regulator.