1a. Objectives (from AD-416)
The goal is to identify mechanisms by which polyamines enhance the accumulation of choline and N-transport amino acids in tomato fruit. Further, we will determine if increased production and quality attributes in tomato plants grown under leguminous cover crop (hairy vetch) involve polyamine-responsive component(s).
1b. Approach (from AD-416)
We will use transgenic technology to develop genotypes enriched in nutrients beneficial for human health. These genotypes will be analyzed for gene expression, particularly to elucidate mechanisms responding to higher polyamines. The interaction of methyl jasmonate with polyamines in regulating fruit metabolism will be analyzed in methyl jasmonate deficient transgenic tomato genotype. Influence of cover crop mulches on gene expression and metabolite profiles will be conducted on field grown transgenic and non-transgenic plants.
3. Progress Report
Tomato is a model horticultural crop for improvement of nutritional quality and long shelf-life. Both the quality attributes and shelf-life are genetically programmed. Tomato fruit and its processed products are dietary source of antioxidants, vitamins and minerals. Ripening is delayed in tomato mutants that accumulate ubiquitous biogenic polyamines, such as putrescine, spermidine and spermine. To gain an insight into the role of polyamines in fruit biology, we genetically altered the levels of spermidine and spermine by over-expressing polyamine biosynthesis genes. Scientists at the ARS’s Sustainable Agricultural Systems Laboratory, Beltsville, Maryland in collaboration with researchers at the Purdue University and at CNR, Rome, Italy have used molecular approaches to identify genes that are specifically expressed at different stages of maturation and ripening of tomato fruit. It was shown that genes that are responsive to abiotic and biotic stresses and to the plant hormone ethylene are upregulated during early stages of fruit ripening. Following this genetic program, the genes involved in metabolism and nutrient accumulation are expressed at higher levels during ripening, and the post ripening phase is characterized by expression of genes that are involved in ubiquitin-mediated protein degradation. These data provide a window into the various cellular processes occurring at different stages of fruit maturation and ripening of tomato. A large proportion (53%) of the genes printed on the macroarray could not be assigned a clear function based on the sequences available in the public databases. These uncharacterized genes hold promise for providing additional tools to modulate process of fruit development and ripening. One of the genes implicated in flavor, taste and nutritional quality of fruits is called lipoxygenase (LOX). Hydroperoxides produced through the action of LOX are subsequently metabolized to a C6 volatile molecule called (Z)-hex-3-enal, which is one of the most valuable aroma components in tomato fruit. To study the role of LOX in tomato metabolism, we genetically silenced the expression of ripening-related LOXs in tomato fruit. The LOX-silenced fruits were found deficient in the production of a stress hormone called methyl jasmonate (MJA). Thirty one fruit metabolites were profiled including different classes of amino acids, organic acids, carbohydrates and other signaling molecules. The levels of a majority of these metabolites were negatively impacted in LOX-silenced transgenic fruit as compared to the wild type line, particularly at the beginning of the ripening process. These data suggest that MJA regulates shift in important molecules during fruit ripening and therefore LOX together with MJA can contribute towards the organoleptic characteristics of a fruit. These data are important to scientists and agriculturists interested in developing novel strategies to further the aroma and taste of fruits.
1. The biochemistry of fruit ripening and the development of associated nutritional and flavor compounds is not well understood. Scientist at the ARS Sustainable Agricultural Systems Laboratory, Beltsville, Maryland, showed that a reduction in the endogenous level of methyl jasmonate (MeJA) significantly affected overall primary metabolism in tomato fruit, mostly a negative effect on the accumulation of specific amino acids. Among them were pigment and aroma generating amino acids that add to flavor and taste of a fruit. These studies, therefore, show that jasmonates including MeJA are important contributors to the flavor and taste of fruits, particularly tomato.
Mattoo, A.K., Shukla, V., Fatima, T., Handa, A.K., Yachha, S.K. 2010. Genetic Engineering to Enhance Crop-Based Phytonutrients (Nutraceuticals) to Alleviate Diet-Related Diseases. In: Giardi, M.T., Rea, G., and Berra, B., editors. Bio-Farms for Nutraceuticals: Functional Food and Safety Control by Biosensors. Austin, TX: Landes Bioscience, Springer. p. 122-143.