Manipulation of <Emphasis Type="SmallCaps">l</Emphasis>-ascorbic acid biosynthesis pathways in <Emphasis Type="Italic">Solanum lycopersicum</Emphasis>: elevated GDP-mannose pyrophosphorylase activity enhances <Emphasis Type="SmallCaps">l</Emphasis>-ascorbate levels in red fruit |
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Authors: | Christelle Cronje Gavin M George Alisdair R Fernie Jan Bekker Jens Kossmann Rolene Bauer |
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Institution: | 1.Genetics Department, Institute for Plant Biotechnology,Stellenbosch University,Matieland,South Africa;2.Max Planck Institute for Molecular Plant Physiology,Potsdam-Golm,Germany;3.Department of Biotechnology, Institute for Microbial Biotechnology and Metagenomics,University of the Western Cape,Cape Town,South Africa |
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Abstract: | Ascorbate (AsA) plays a fundamental role in redox homeostasis in plants and animals, primarily by scavenging reactive oxygen
species. Three genes, representing diverse steps putatively involved in plant AsA biosynthesis pathways, were cloned and independently
expressed in Solanum lycopersicum (tomato) under the control of the CaMV 35S promoter. Yeast-derived GDP-mannose pyrophosphorylase (GMPase) and arabinono-1,4-lactone oxidase (ALO), as well as myo-inositol oxygenase 2 (MIOX2) from Arabidopsis thaliana, were targeted. Increases in GMPase activity were concomitant with increased AsA levels of up to 70% in leaves, 50% in green
fruit, and 35% in red fruit. Expression of ALO significantly pulled biosynthetic flux towards AsA in leaves and green fruit by up to 54 and 25%, respectively. Changes in
AsA content in plants transcribing the MIOX2 gene were inconsistent in different tissue. On the other hand, MIOX activity was strongly correlated with cell wall uronic
acid levels, suggesting that MIOX may be a useful tool for the manipulation of cell wall composition. In conclusion, the Smirnoff–Wheeler
pathway showed great promise as a target for biotechnological manipulation of ascorbate levels in tomato. |
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