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Submitted to: Biology and Biotechology of the Plant Hormone Ethylene
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 12/10/2002 Publication Date: 3/10/2003 Citation: Mattoo, A.K., Cassol, T., Mehta, R.A., Goyal, R., Neelam, A., Chung, S.-H., Kumar, V., and Handa, A. 2003. Lessons one can learn from studying transgenic tomatoes that accumulate higher polyamines in a ripening-specific manner. In: M. Vendrell, H. Klee, J.C. Pech and F. Romojaro, editors. Biology and Biotechnology of the Plant Hormone Ethylene III. Amsterdam:IOS Press. p. 359-364. Interpretive Summary: We are studying the processes that control accumulation of phytonutrients in tomato fruit in order to enhance their levels to develop nutritious produce. To do this, we have developed a tomato that was genetically engineered to accumulate particular plant growth substances called polyamines. These nitrogenous compounds have been considered beneficial for agriculture but direct evidence for their involvement in any particular process had not been presented until now. The high-polyamine tomatoes accumulate 300 percent more lycopene, an antioxidant that is reported to prevent breast and prostate cancer and enhance cardiovascular health. We are further analyzing these fruits to pinpoint the mechanisms by which polyamines do the good things we find they do. This manuscript summarizes our findings and presents a scenario of lessons we could learn from analyzing the high-lycopene and high-polyamine transgenic tomato. This work is of interest to academic scientists and fruit and vegetable industry researchers who would like to develop value-added produce. Technical Abstract: S-adenosylmethionine (SAM) is a key intermediate in the ethylene and polyamine biosynthesis pathways. Based on studies using inhibitors of each of these two pathways and following flux of the common, radiolabeled precursors, a cross talk between the two pathways has been hypothesized. However, it is not known if the endogenous pools of SAM influence biosynthesis of ethylene or that of polyamines. To determine a physiological function of endogenous polyamines and delineate between polyamine and ethylene dependent processes, we have expressed a yeast SAM decarboxylase in tomato fruit in a fruit-specific manner via the fruit specific promoter E8. Multiple independent transgenic plants and their progenies were characterized for physiological, biochemical and phenotypic attributes to assess in planta the roles of higher polyamines, spermidine and spermine. Transgenic ripening tomato fruits accumulated several-fold higher levels of spermidine and spermine indicating that the yeast SAM decarboxylase ySAMdc) gene is functional in plants. Fruits homozygous with ySAMdc gene had a longer vine life and 300% enhancement in the lycopene content, suggesting that polyamines influence diverse physiological processes. High-polyamines fruit also had enhanced ethylene production rates, indicating that SAM levels are not limiting in a ripening tomato fruit. Subtractive cloning and macroarray approaches are being used to evaluate global gene expression that polyamines influence in tomato fruit. |
