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Jain, Ashok Kumar; Nessler, Craig L.

doi:10.1023/a:1009680818138

Cited by 161 publications

(34 citation statements)

References 23 publications

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“…The enzyme (GLDH) overexpressed in this study is highlighted, and the chemical structure of substrates for the final steps and the product (AsA) is shown of the transgene was confirmed, and the resultant AsA content showed variations depending on the studies. GLOoverexpressing tobacco or lettuce plants led to a 5-to 7-fold increase in the AsA content (Jain and Nessler 2000), while GDH-overexpressing tobacco did not show any increase (Gatzek et al 2002). In other cases, 1.5-to 3-fold elevations were observed (Ishikawa et al 2006;Wolucka and Van Montagu 2007).…”

Section: Introductionmentioning

confidence: 86%

“…Attempts to enhance the AsA content in transgenic plants by overexpression of the genes in the AsA biosynthetic pathway, including GLO (Jain and Nessler 2000;Radzio et al 2003), Gal dehydrogenase (GDH) (Gatzek et al 2002), aldo-keto reductase (AKR) (Agius et al 2003), myo-inositol oxygenase (MIO) (Lorence et al 2004), and GLDH (Tokunaga et al 2005), have been reported so far (indicated by boxes in Fig. 1).…”

Section: Introductionmentioning

confidence: 99%

“…Despite the significant increase in the AsA content in GLO-overexpressing tobacco (Jain and Nessler 2000), the GLDH activity seems to influence the AsA content; this is suggested by the observation that AsA formation from exogenously supplied GulL is lower than that from exogenous GalL, a substrate for GLDH (Davey et al 1999;Pallanca and Smirnoff 1999), demonstrated in Arabidopsis cultured cells and pea embryonic axes. Similarly, in GLO-overexpressing tobacco leaves, GalL feeding resulted in 3-to 4-fold higher AsA accumulation than GulL feeding (Jain and Nessler 2000).…”

Section: Introductionmentioning

confidence: 99%

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Importance of the l-galactonolactone pool for enhancing the ascorbate content revealed by l -galactonolactone dehydrogenase-overexpressing tobacco plants

Imai

Niwa

Ban

et al. 2008

Plant Cell Tiss Organ Cult

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L-Galactono-1,4-lactone (GalL) dehydrogenase (GLDH) is an enzyme that catalyzes the last step of L-ascorbate (AsA) biosynthesis in plants. To re-evaluate the importance of the enzyme and the possibility of manipulating the AsA content in plants, a cDNA encoding GLDH from sweet potato was introduced into tobacco plants by Agrobacterium-mediated transformation under the control of a CaMV 35S promoter. Protein blot analysis revealed the elevation of GLDH protein contents in three GLDH-transformed lines. Furthermore, these transgenic lines showed 6-to 10-fold higher GLDH activities in the roots than the non-transformed plants, SR1. Despite the elevated GLDH activity, the AsA content in the leaves did not change in all lines; i.e., the AsA content in GLDH-transformed lines was 3-7 lmol g -1 FW, comparable to that in the non-transformed plants. Incubation of leaf discs in a GalL solution led to a rapid 2-to 3-fold increase in the AsA content in both GLDH-transformed and non-transformed plants in the same manner. These results suggest that the supply of GalL is a crucial factor for determining the AsA pool size and that the upstream genes in the AsA biosynthetic pathway are responsible for enhancing the AsA content in plants.

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Section: Introductionmentioning

confidence: 86%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Importance of the l-galactonolactone pool for enhancing the ascorbate content revealed by l -galactonolactone dehydrogenase-overexpressing tobacco plants

Imai

Niwa

Ban

et al. 2008

Plant Cell Tiss Organ Cult

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“…Plants, algae, and the majority of animals are able to synthesize vitamin C. Humans, however, lack L-gulono-1,4-lactone oxidase, the last enzyme of the vitamin C pathway in animals, and require L-AA as an essential micronutrient. L-AA biosynthetic genes can be engineered to increase vitamin C content of plants (3)(4), in view of improving the nutritional value and stress resistance of crops, but also potentially exploited for the industrial production of vitamin C (5).…”

mentioning

confidence: 99%

GDP-Mannose 3′,5′-Epimerase Forms GDP-L-gulose, a Putative Intermediate for the de Novo Biosynthesis of Vitamin C in Plants

Wolucka

Montagu

2003

Journal of Biological Chemistry

346

323

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Despite its importance for agriculture, bioindustry, and nutrition, the fundamental process of L-ascorbic acid (vitamin C) biosynthesis in plants is not completely elucidated, and little is known about its regulation. The recently identified GDP-Man 3,5-epimerase catalyzes a reversible epimerization of GDP-D-mannose that precedes the committed step in the biosynthesis of vitamin C, resulting in the hydrolysis of the highly energetic glycosyl-pyrophosphoryl linkage. Here, we characterize the native and recombinant GDP-Man 3,5-epimerase of Arabidopsis thaliana. GDP and GDP-D-glucose are potent competitive inhibitors of the enzyme, whereas GDP-L-fucose gives a complex type of inhibition. The epimerase contains a modified version of the NAD binding motif and is inhibited by NAD(P)H and stimulated by NAD(P) ؉ . A feedback inhibition of vitamin C biosynthesis is observed apparently at the level of GDP-Man 3,5-epimerase. The epimerase catalyzes at least two distinct epimerization reactions and releases, besides the well known GDP-L-galactose, a novel intermediate: GDP-Lgulose. The yield of the epimerization varies and seems to depend on the molecular form of the enzyme. Both recombinant and native enzymes co-purified with a Hsp70 heat-shock protein (Escherichia coli DnaK and A. thaliana Hsc70.3, respectively). We speculate, therefore, that the Hsp70 molecular chaperones might be involved in folding and/or regulation of the epimerase. In summary, the plant epimerase undergoes a complex regulation and could control the carbon flux into the vitamin C pathway in response to the redox state of the cell, stress conditions, and GDP-sugar demand for the cell wall/glycoprotein biosynthesis. Exogenous L-gulose and L-gulono-1,4-lactone serve as direct precursors of L-ascorbic acid in plant cells. We propose an L-gulose pathway for the de novo biosynthesis of vitamin C in plants.Vitamin C (L-ascorbic acid (L-AA) 1 ) acts as an enzyme cofactor and an antioxidant. In plants it may represent one of the major soluble carbohydrates and is involved in crucial physiological processes such as biosynthesis of the cell wall, phytohormones, and secondary metabolites, cell division and growth, and stress resistance and photoprotection (for review, see Ref.1). Large variations in vitamin C content (from 0.003 to 1% of fresh weight; w/w), reported for different plant species, organs, and tissues (2), are intimately linked to the vitamin biosynthesis, stability, and function. Plants, algae, and the majority of animals are able to synthesize vitamin C. Humans, however, lack L-gulono-1,4-lactone oxidase, the last enzyme of the vitamin C pathway in animals, and require L-AA as an essential micronutrient. L-AA biosynthetic genes can be engineered to increase vitamin C content of plants (3-4), in view of improving the nutritional value and stress resistance of crops, but also potentially exploited for the industrial production of vitamin C (5).The biosynthesis of vitamin C in plants is not completely elucidated, and its regulation is largely unknown....

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“…Plants expressing L-gulono-1,4-lactone oxidoreductase from rat were reported to contain elevated AsA, although the pathway by which this occurred is unknown, and whether the ascorbate redox state was altered was not reported (13). Although AsA biosynthetic mutants have been described (14)(15)(16)(17), there has been no report of increasing AsA levels and redox state through the manipulation of the plant-specific pathway.…”

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confidence: 99%

Increasing vitamin C content of plants through enhanced ascorbate recycling

Zhong

Young

Ling

et al. 2003

Proc. Natl. Acad. Sci. U.S.A.

473

294

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Vitamin C (ascorbic acid) is essential to prevent disease associated with connective tissue (e.g., scurvy), improves cardiovascular and immune cell functions, and is used to regenerate ␣-tocopherol (vitamin E). In contrast to most animals, humans lack the ability to synthesize ascorbic acid as a result of a mutation in the last enzyme required for ascorbate biosynthesis. Vitamin C, therefore, must be obtained from dietary sources and, because it cannot be stored in the body, it must be obtained regularly. Once used, ascorbic acid can be regenerated from its oxidized form in a reaction catalyzed by dehydroascorbate reductase (DHAR). To examine whether overexpression of DHAR in plants would increase the level of ascorbic acid through improved ascorbate recycling, a DHAR cDNA from wheat was isolated and expressed in tobacco and maize, where DHAR expression was increased up to 32-and 100-fold, respectively. The increase in DHAR expression increased foliar and kernel ascorbic acid levels 2-to 4-fold and significantly increased the ascorbate redox state in both tobacco and maize. In addition, the level of glutathione, the reductant used by DHAR, also increased, as did its redox state. These results demonstrate that the vitamin C content of plants can be elevated by increasing expression of the enzyme responsible for recycling ascorbate.ascorbic acid ͉ dehydroascorbate reductase ͉ redox state ͉ glutathione ͉ nutrition

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Cited by 161 publications

References 23 publications

Importance of the l-galactonolactone pool for enhancing the ascorbate content revealed by l -galactonolactone dehydrogenase-overexpressing tobacco plants

Importance of the l-galactonolactone pool for enhancing the ascorbate content revealed by l -galactonolactone dehydrogenase-overexpressing tobacco plants

GDP-Mannose 3′,5′-Epimerase Forms GDP-L-gulose, a Putative Intermediate for the de Novo Biosynthesis of Vitamin C in Plants

Increasing vitamin C content of plants through enhanced ascorbate recycling

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