Folate biofortification of tomato fruit

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 104; no. 10; pp. 4218 - 4222
• Main Authors: Díaz de la Garza, Rocío I, Gregory, Jesse F. III, Hanson, Andrew D
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 06.03.2007; National Acad Sciences
• Series: From the Cover
• Subjects: Actins; aminodeoxychorismate synthase; biochemical pathways; biofortification; Biological Sciences; Biosynthesis; Botany; Carbon - metabolism; Carbon-Nitrogen Ligases - biosynthesis; Carbon-Nitrogen Ligases - genetics; Crosses, Genetic; Enzymes; Ethylenes - pharmacology; Fluorescence; folic acid; Folic Acid - metabolism; food composition; food fortification; Food, Fortified; fortified foods; Fruits; gene overexpression; Genetic Engineering - methods; Genetic Techniques; Genetic Vectors; Lycopersicon esculentum; Lycopersicon esculentum - metabolism; p-aminobenzoic acid; Plants; Plants, Genetically Modified; Polymerase chain reaction; Pteridines; Pteridines - metabolism; Ripening; RNA, Plant - metabolism; Solanum lycopersicum var. lycopersicum; Tetrahydrofolates - pharmacology; Tomatoes; Transaminases; Transgenic plants; Vitamin B; vitamin content; Vitamins - metabolism
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0700409104

Folate deficiency leads to neural tube defects and other human diseases, and is a global health problem. Because plants are major folate sources for humans, we have sought to enhance plant folate levels (biofortification). Folates are synthesized from pteridine, p-aminobenzoate (PABA), and glutamate precursors. Previously, we increased pteridine production in tomato fruit up to 140-fold by overexpressing GTP cyclohydrolase I, the first enzyme of pteridine synthesis. This strategy increased folate levels 2-fold, but engineered fruit were PABA-depleted. We report here the engineering of fruit-specific overexpression of aminodeoxychorismate synthase, which catalyzes the first step of PABA synthesis. The resulting fruit contained an average of 19-fold more PABA than controls. When transgenic PABA- and pteridine-overproduction traits were combined by crossing, vine-ripened fruit accumulated up to 25-fold more folate than controls. Folate accumulation was almost as high (up to 15-fold) in fruit harvested green and ripened by ethylene-gassing, as occurs in commerce. The accumulated folates showed normal proportions of one-carbon forms, with 5-methyltetrahydrofolate the most abundant, but were less extensively polyglutamylated than controls. Folate concentrations in developing fruit did not change in controls, but increased continuously throughout ripening in transgenic fruit. Pteridine and PABA levels in transgenic fruit were >20-fold higher than in controls, but the pathway intermediates dihydropteroate and dihydrofolate did not accumulate, pointing to a flux constraint at the dihydropteroate synthesis step. The folate levels we achieved provide the complete adult daily requirement in less than one standard serving.