title: Manipulation of L-ascorbic acid biosynthesis pathways in Solanum lycopersicum: elevated GDP-mannose pyrophosphorylase activity enhances L-ascorbate levels in red fruit.
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.
authors: Genetics Department, Institute for Plant Biotechnology, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa.
authors: Christelle
authors: C
authors: Cronje
authors: Gavin M
authors: GM
authors: George
authors: Alisdair R
authors: AR
authors: Fernie
authors: Jan
authors: J
authors: Bekker
authors: Jens
authors: J
authors: Kossmann
authors: Rolene
authors: R
authors: Bauer
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D001205:Ascorbic Acid / Q000096:biosynthesis*; D005638:Fruit / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D050562:Inositol Oxygenase / Q000235:genetics / Q000378:metabolism; D018551:Solanum lycopersicum / Q000235:genetics / Q000378:metabolism*; D008954:Models, Biological; D009713:Nucleotidyltransferases / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism
chemical_list: D050562:Inositol Oxygenase; D009713:Nucleotidyltransferases; C026917:mannose 1-phosphate guanylyltransferase; D001205:Ascorbic Acid