Altered Levels of Aroma and Volatiles by Metabolic Engineering of Shikimate Pathway Genes in Tomato Fruits

Vered Tzin; Ilana Rogachev; Sagit Meir; Michal Moyal Ben Zvi; Tania Masci; Alexander Vainstein; Asaph Aharoni; Gad Galili; Vered Tzin; Ilana Rogachev; Sagit Meir; Michal Moyal Ben Zvi; Tania Masci; Alexander Vainstein; Asaph Aharoni; Gad Galili

doi:10.3934/bioeng.2015.2.75

AIMS Bioengineering

2015, Volume 2, Issue 2: 75-92. doi: 10.3934/bioeng.2015.2.75

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Altered Levels of Aroma and Volatiles by Metabolic Engineering of Shikimate Pathway Genes in Tomato Fruits

1.
Department of Plant Sciences, The Weizmann Institute of Science, PO Box 26, Rehovot 76100, Israel;
2.
The Institute of Plant Sciences and Genetics in Agriculture, Faculty of Agricultural, The Hebrew University of Jerusalem, PO Box 12, Rehovot 76100, Israel;
3.
The Boyce Thompson Institute for Plant Research, Ithaca, NY 14853, USA;
4.
AB Seeds Ltd, PO Box 1 Misgav Ind. Area 2017900, Israel

Received: 18 April 2015 Accepted: 16 June 2015 Published: 18 June 2015

The tomato (Solanum lycopersicum) fruit is an excellent source of antioxidants, dietary fibers, minerals and vitamins and therefore has been referred to as a “functional food”. Ripe tomato fruits produce a large number of specialized metabolites including volatile organic compounds. These volatiles serve as key components of the tomato fruit flavor, participate in plant pathogen and herbivore defense, and are used to attract seed dispersers. A major class of specialized metabolites is derived from the shikimate pathway followed by aromatic amino acid biosynthesis of phenylalanine, tyrosine and tryptophan. We attempted to modify tomato fruit flavor by overexpressing key regulatory genes in the shikimate pathway. Bacterial genes encoding feedback-insensitive variants of 3-Deoxy-D-Arabino-Heptulosonate 7-Phosphate Synthase (DAHPS; AroG_209-9) and bi-functional Chorismate Mutase/Prephenate Dehydratase (CM/PDT; PheA₁₂) were expressed under the control of a fruit-specific promoter. We crossed these transgenes to generate tomato plants expressing both the AroG₂₀₉ and PheA₁₂ genes. Overexpression of the AroG_209-9 gene had a dramatic effect on the overall metabolic profile of the fruit, including enhanced levels of multiple volatile and non-volatile metabolites. In contrast, the PheA₁₂ overexpression line exhibited minor metabolic effects compared to the wild type fruit. Co-expression of both the AroG_209-9 and PheA₁₂genesin tomato resulted overall in a similar metabolic effect to that of expressing only the AroG_209-9gene. However, the aroma ranking attributes of the tomato fruits from PheA₁₂//AroG_209-9 were unique and different from those of the lines expressing a single gene, suggesting a contribution of the PheA₁₂ gene to the overall metabolic profile. We suggest that expression of bacterial genes encoding feedback-insensitive enzymes of the shikimate pathway in tomato fruits provides a useful metabolic engineering tool for the modification of fruits aroma and the generation of new combinations of tomato flavors.
- 3-Deoxy-D-Arabino-Heptulosonate 7-Phosphate Synthase,
- aromatic amino acids,
- metabolism,
- volatiles,
- Chorismate Mutase,
- Prephenate Dehydratase
Citation: Vered Tzin, Ilana Rogachev, Sagit Meir, Michal Moyal Ben Zvi, Tania Masci, Alexander Vainstein, Asaph Aharoni, Gad Galili. Altered Levels of Aroma and Volatiles by Metabolic Engineering of Shikimate Pathway Genes in Tomato Fruits[J]. AIMS Bioengineering, 2015, 2(2): 75-92. doi: 10.3934/bioeng.2015.2.75

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Abstract

The tomato (Solanum lycopersicum) fruit is an excellent source of antioxidants, dietary fibers, minerals and vitamins and therefore has been referred to as a “functional food”. Ripe tomato fruits produce a large number of specialized metabolites including volatile organic compounds. These volatiles serve as key components of the tomato fruit flavor, participate in plant pathogen and herbivore defense, and are used to attract seed dispersers. A major class of specialized metabolites is derived from the shikimate pathway followed by aromatic amino acid biosynthesis of phenylalanine, tyrosine and tryptophan. We attempted to modify tomato fruit flavor by overexpressing key regulatory genes in the shikimate pathway. Bacterial genes encoding feedback-insensitive variants of 3-Deoxy-D-Arabino-Heptulosonate 7-Phosphate Synthase (DAHPS; AroG_209-9) and bi-functional Chorismate Mutase/Prephenate Dehydratase (CM/PDT; PheA₁₂) were expressed under the control of a fruit-specific promoter. We crossed these transgenes to generate tomato plants expressing both the AroG₂₀₉ and PheA₁₂ genes. Overexpression of the AroG_209-9 gene had a dramatic effect on the overall metabolic profile of the fruit, including enhanced levels of multiple volatile and non-volatile metabolites. In contrast, the PheA₁₂ overexpression line exhibited minor metabolic effects compared to the wild type fruit. Co-expression of both the AroG_209-9 and PheA₁₂genesin tomato resulted overall in a similar metabolic effect to that of expressing only the AroG_209-9gene. However, the aroma ranking attributes of the tomato fruits from PheA₁₂//AroG_209-9 were unique and different from those of the lines expressing a single gene, suggesting a contribution of the PheA₁₂ gene to the overall metabolic profile. We suggest that expression of bacterial genes encoding feedback-insensitive enzymes of the shikimate pathway in tomato fruits provides a useful metabolic engineering tool for the modification of fruits aroma and the generation of new combinations of tomato flavors.

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