Submitted to: Plant Biotechnology Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2007
Publication Date: 3/15/2007
Citation: Mattoo, A.K., Srivastava, A., Chung, S.H., Fatima, T., Datsenka, T., Handa, A. 2007. Polyamines as anabolic growth regulators revealed by transcriptome analysis and metabolite profiles of tomato fruits engineered to accumulate spermidine and spermine. Plant Biotechnology Journal. 24:57-70. Interpretive Summary: Tomato is one of the most consumed vegetable/fruit crops and is an important dietary source of vitamins, minerals and fiber. The levels of nutrients in a red ripe fruit are not at par with the recommended daily allowance for vitamins and minerals. We are using molecular engineering technology to identify key genes that determine nutritional quality of tomato fruit. We have developed genetically enhanced tomato fruits with improved juice quality and delayed ripening on the vine by enabling fruit-specific expression of the yeast SAMdc in transgenic tomatoes. Metabolite profiles of these fruit that accumulate higher polyamines, spermidine and spermine showed that these molecules initiate anabolic and nitrogen-carbon interactions, positively impacting nutrient composition. In this study, we have used an array of 1066 genes and provide evidence that 266 unigenes of these are differentially expressed in the high polyamine tomatoes compared to the control wild-type fruit. We also show concurrence between the differences in nutrient metabolism and the regulation of the gene transcripts. These data show for the first time that polyamines act as anabolic growth regulators. These results are important to scientists, breeders, and researchers interested in understanding pathways by which a fruit’s nutrient levels are elevated.
Technical Abstract: 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 wild 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.