title: Enhancing ascorbate in fruits and tubers through over-expression of the L-galactose pathway gene GDP-L-galactose phosphorylase.
abstract: Ascorbate, or vitamin C, is obtained by humans mostly from plant sources. Various approaches have been made to increase ascorbate in plants by transgenic means. Most of these attempts have involved leaf material from model plants, with little success reported using genes from the generally accepted l-galactose pathway of ascorbate biosynthesis. We focused on increasing ascorbate in commercially significant edible plant organs using a gene, GDP-l-galactose phosphorylase (GGP or VTC2), that we had previously shown to increase ascorbate concentration in tobacco and Arabidopsis thaliana. The coding sequence of Actinidia chinensis GGP, under the control of the 35S promoter, was expressed in tomato and strawberry. Potato was transformed with potato or Arabidopsis GGP genes under the control of the 35S promoter or a polyubiquitin promoter (potato only). Five lines of tomato, up to nine lines of potato, and eight lines of strawberry were regenerated for each construct. Three lines of tomato had a threefold to sixfold increase in fruit ascorbate, and all lines of strawberry showed a twofold increase. All but one line of each potato construct also showed an increase in tuber ascorbate of up to threefold. Interestingly, in tomato fruit, increased ascorbate was associated with loss of seed and the jelly of locular tissue surrounding the seed which was not seen in strawberry. In both strawberry and tomato, an increase in polyphenolic content was associated with increased ascorbate. These results show that GGP can be used to raise significantly ascorbate concentration in commercially significant edible crops.
authors: The New Zealand Institute for Plant and Food Research Limited, Auckland, New Zealand.
authors: Sean
authors: S
authors: Bulley
authors: Michele
authors: M
authors: Wright
authors: Caius
authors: C
authors: Rommens
authors: Hua
authors: H
authors: Yan
authors: Maysoon
authors: M
authors: Rassam
authors: Kui
authors: K
authors: Lin-Wang
authors: Christelle
authors: C
authors: Andre
authors: Di
authors: D
authors: Brewster
authors: Sakuntala
authors: S
authors: Karunairetnam
authors: Andrew C
authors: AC
authors: Allan
authors: William A
authors: WA
authors: Laing
mesh_terms: D029042:Actinidia / Q000201:enzymology; D000595:Amino Acid Sequence; D001205:Ascorbic Acid / Q000378:metabolism*; D053898:Biosynthetic Pathways / Q000235:genetics*; D031985:Fragaria / Q000235:genetics; D005638:Fruit / Q000033:anatomy & histology / Q000201:enzymology / Q000378:metabolism*; D005690:Galactose / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant / Q000235:genetics; D006153:Guanosine Diphosphate / Q000378:metabolism*; D018551:Solanum lycopersicum / Q000235:genetics; D008969:Molecular Sequence Data; D009929:Organ Size; D010744:Phosphoric Monoester Hydrolases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D018515:Plant Leaves / Q000033:anatomy & histology; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D035281:Plant Tubers / Q000201:enzymology / Q000378:metabolism*; D030821:Plants, Genetically Modified; D016415:Sequence Alignment; D011198:Solanum tuberosum / Q000235:genetics
chemical_list: D010940:Plant Proteins; D006153:Guanosine Diphosphate; D010744:Phosphoric Monoester Hydrolases; D001205:Ascorbic Acid; D005690:Galactose