The <i>Myo</i>‐inositol pathway does not contribute to ascorbic acid synthesis

Kavková, Eva; Blöchl, Constantin; Tenhaken, Raimund

doi:10.1111/plb.12898

Cited by 42 publications

(22 citation statements)

References 34 publications

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“…Arabidopsis plants overexpressing MIOX4 showed a 2-3-fold ascorbate content (Lorence et al, 2004). However, based on early radiotracer experiments (Loewus, 1963) and more recent reports (Endres and Tenhaken, 2009, 2011; Ivanov Kavkova et al, 2018), its contribution to the ascorbate pool remains unclear. The second is through the D-galacturonate pathway.…”

Section: Biosynthesis and Metabolism Of Ascorbate In Plantsmentioning

confidence: 99%

Vitamin C Content in Fruits: Biosynthesis and Regulation

et al. 2019

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Throughout evolution, a number of animals including humans have lost the ability to synthesize ascorbic acid (ascorbate, vitamin C), an essential molecule in the physiology of animals and plants. In addition to its main role as an antioxidant and cofactor in redox reactions, recent reports have shown an important role of ascorbate in the activation of epigenetic mechanisms controlling cell differentiation, dysregulation of which can lead to the development of certain types of cancer. Although fruits and vegetables constitute the main source of ascorbate in the human diet, rising its content has not been a major breeding goal, despite the large inter- and intraspecific variation in ascorbate content in fruit crops. Nowadays, there is an increasing interest to boost ascorbate content, not only to improve fruit quality but also to generate crops with elevated stress tolerance. Several attempts to increase ascorbate in fruits have achieved fairly good results but, in some cases, detrimental effects in fruit development also occur, likely due to the interaction between the biosynthesis of ascorbate and components of the cell wall. Plants synthesize ascorbate de novo mainly through the Smirnoff-Wheeler pathway, the dominant pathway in photosynthetic tissues. Two intermediates of the Smirnoff-Wheeler pathway, GDP-D-mannose and GDP-L-galactose, are also precursors of the non-cellulosic components of the plant cell wall. Therefore, a better understanding of ascorbate biosynthesis and regulation is essential for generation of improved fruits without developmental side effects. This is likely to involve a yet unknown tight regulation enabling plant growth and development, without impairing the cell redox state modulated by ascorbate pool. In certain fruits and developmental conditions, an alternative pathway from D-galacturonate might be also relevant. We here review the regulation of ascorbate synthesis, its close connection with the cell wall, as well as different strategies to increase its content in plants, with a special focus on fruits.

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Section: Biosynthesis and Metabolism Of Ascorbate In Plantsmentioning

confidence: 99%

Vitamin C Content in Fruits: Biosynthesis and Regulation

et al. 2019

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“…A myoinositol oxygenase (MIOX4) has been identified in Arabidopsis [123]. However, the effective contribution of myoinositol to vitamin C synthesis in vivo is strongly debated [167,168,169].…”

Section: Vitamin C Biosynthesis In Plantsmentioning

confidence: 99%

Vitamin C in Plants: From Functions to Biofortification

et al. 2019

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Vitamin C (l-ascorbic acid) is an excellent free radical scavenger, not only for its capability to donate reducing equivalents but also for the relative stability of the derived monodehydroascorbate radical. However, vitamin C is not only an antioxidant, since it is also a cofactor for numerous enzymes involved in plant and human metabolism. In humans, vitamin C takes part in various physiological processes, such as iron absorption, collagen synthesis, immune stimulation, and epigenetic regulation. Due to the functional loss of the gene coding for l-gulonolactone oxidase, humans cannot synthesize vitamin C; thus, they principally utilize plant-based foods for their needs. For this reason, increasing the vitamin C content of crops could have helpful effects on human health. To achieve this objective, exhaustive knowledge of the metabolism and functions of vitamin C in plants is needed. In this review, the multiple roles of vitamin C in plant physiology as well as the regulation of its content, through biosynthetic or recycling pathways, are analyzed. Finally, attention is paid to the strategies that have been used to increase the content of vitamin C in crops, emphasizing not only the improvement of nutritional value of the crops but also the acquisition of plant stress resistance.

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“…Knockout of GlcAK1 ought to increase the flux from myo-inositol to ascorbate if the myo-inositol pathway is operational; however, no changes in ascorbate concentrations were detected in the Arabidopsis glcak1 mutants. Moreover, radiolabeled 3 H-myo-inositol in the Arabidopsis glcak1 mutants accumulated as D-gluconorate and ascorbate remained unlabeled, leading the authors to conclude that the myo-inositol pathway does not contribute towards ascorbate biosynthesis in plants [71].…”

Section: The Myo-inositol Pathwaymentioning

confidence: 99%

Manipulation of Ascorbate Biosynthetic, Recycling, and Regulatory Pathways for Improved Abiotic Stress Tolerance in Plants

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Bonneau

Hellens

et al. 2020

IJMS

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Abiotic stresses, such as drought, salinity, and extreme temperatures, are major limiting factors in global crop productivity and are predicted to be exacerbated by climate change. The overproduction of reactive oxygen species (ROS) is a common consequence of many abiotic stresses. Ascorbate, also known as vitamin C, is the most abundant water-soluble antioxidant in plant cells and can combat oxidative stress directly as a ROS scavenger, or through the ascorbate–glutathione cycle—a major antioxidant system in plant cells. Engineering crops with enhanced ascorbate concentrations therefore has the potential to promote broad abiotic stress tolerance. Three distinct strategies have been utilized to increase ascorbate concentrations in plants: (i) increased biosynthesis, (ii) enhanced recycling, or (iii) modulating regulatory factors. Here, we review the genetic pathways underlying ascorbate biosynthesis, recycling, and regulation in plants, including a summary of all metabolic engineering strategies utilized to date to increase ascorbate concentrations in model and crop species. We then highlight transgene-free strategies utilizing genome editing tools to increase ascorbate concentrations in crops, such as editing the highly conserved upstream open reading frame that controls translation of the GDP-L-galactose phosphorylase gene.

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The Myo‐inositol pathway does not contribute to ascorbic acid synthesis

Cited by 42 publications

References 34 publications

Vitamin C Content in Fruits: Biosynthesis and Regulation

Vitamin C Content in Fruits: Biosynthesis and Regulation

Vitamin C in Plants: From Functions to Biofortification

Manipulation of Ascorbate Biosynthetic, Recycling, and Regulatory Pathways for Improved Abiotic Stress Tolerance in Plants

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