Upregulation of pyrophosphate: fructose 6-phosphate 1-phosphotransferase (PFP) activity in strawberry |
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Authors: | C E Basson J-H Groenewald J Kossmann C Cronjé R Bauer |
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Institution: | (1) Institute for Plant Biotechnology, Genetics Department, Stellenbosch University, Private Bag X1 Matieland, Stellenbosch, 7602, South Africa;(2) Present address: Institute for Microbial Biotechnology and Metagenomics, Department of Biotechnology, University of the Western Cape, Private Bag X17, Bellville, 7535, South Africa;(3) Institute for Wine Biotechnology, Department of Viticulture and Oenology, Stellenbosch University, Private Bag X1, Matieland, Stellenbosch, 7602, South Africa;(4) Biosafety South Africa, 105 Wentworth, Somerset Links Office Park, De Beers Avenue, Somerset West, 7130, South Africa; |
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Abstract: | Pyrophosphate: fructose 6-phosphate 1-phosphotransferase (PFP) is a cytosolic enzyme catalyzing the first committed step in
glycolysis by reversibly phosphorylating fructose-6-phosphate to fructose-1,6-bisphosphate. The position of PFP in glycolytic
and gluconeogenic metabolism, as well as activity patterns in ripening strawberry, suggest that the enzyme may influence carbohydrate
allocation to sugars and organic acids. Fructose-2,6-bisphosphate activates and tightly regulates PFP activity in plants and
has hampered attempts to increase PFP activity through overexpression. Heterologous expression of a homodimeric isoform from
Giardia lamblia, not regulated by fructose-2,6-bisphosphate, was therefore employed to ensure in vivo increases in PFP activity. The coding
sequence was placed into a constitutive expression cassette under control of the cauliflower mosaic virus 35S promoter and
introduced into strawberry by Agrobacterium tumefaciens-mediated transformation. Heterologous expression of PFP resulted in an up to eightfold increase in total activity in ripe
berries collected over two consecutive growing seasons. Total sugar and organic acid content of transgenic berries harvested
during the first season were not affected when compared to the wild type, however, fructose content increased at the expense
of sucrose. In the second season, total sugar content and composition remained unchanged while the citrate content increased
slightly. Considering that PFP catalyses a reversible reaction, PFP activity appears to shift between gluconeogenic and glycolytic
metabolism, depending on the metabolic status of the cell. |
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