Ascorbate biosynthesis and its involvement in stress tolerance and plant development in rice (Oryza sativa L.)

Abstract

Ascorbic acid (AsA) biosynthesis and its implications for stress tolerance and plant development were investigated in a set of rice knock-out (KO) mutants for AsA biosynthetic genes and their wild-types. KO of two isoforms of GDP-D-mannose epimerase (OsGME) reduced the foliar AsA level by 20-30%, and KO of GDP-L-galactose phosphorylase (OsGGP) by 80%, while KO of myo-inositol oxygenase (OsMIOX) did not affect foliar AsA levels. AsA concentration was negatively correlated with lipid peroxidation in foliar tissue under ozone stress and zinc deficiency, but did not affect the sensitivity to iron toxicity. Lack of AsA reduced the photosynthetic efficiency as represented by the maximum carboxylation rate of Rubisco (Vmax), the maximum electron transport rate (Jmax) and the chlorophyll fluorescence parameter ΦPSII. Mutants showed lower biomass production than their wild-types, especially when OsGGP was lacking (around 80% reductions). All plants except for KO mutants of OsGGP showed distinct peaks in foliar AsA concentrations during the growth, which were consistent with up-regulation of OsGGP, suggesting that OsGGP plays a pivotal role in regulating foliar AsA levels during different growth stages. In conclusion, our data demonstrate multiple roles of AsA in stress tolerance and development of rice.

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

“…For example, increased expression of the MIOX gene in Arabidopsis [67] and rice [68] did not change ascorbate concentrations, despite the Arabidopsis lines with increased MIOX expression having higher MIOX enzymatic activity (Table 1). Further, loss-of-function mutations in the Arabidopsis [69] and rice [70] MIOX genes did not change ascorbate concentrations relative to wild-type, challenging the view that the myo-inositol pathway contributes towards ascorbate biosynthesis. Further opposition comes from a recent study utilizing CRISPR/Cas9-induced knockout mutations in the Arabidopsis glucuronokinase1 (GlcAK1) gene and radiotracer experiments with 3 H-myo-inositol.…”

Low pH altered salt stress in antioxidant metabolism and nitrogen assimilation in ginger (Zingiber officinale) seedlings

“…The accumulation of reactive oxygen species has been reported to hamper many important biological functions, such as photosynthesis, respiration and nutrient uptake (Ahmad et al , Ahanger and Agarwal , Guo et al ), which in turn induced serious oxidative damage to plants. However, to cope with the increased ROS levels, plants have a complex antioxidant defense system that involves non‐enzymatic antioxidants, including ascorbate (AsA) and glutathione (GSH), and enzymes in the ascorbate‐glutathione (AsA‐GSH) cycle, such as ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) and glutathione reductase (GR), which neutralize the effects of stress‐generated ROS (Holler et al , Nahar et al , Hossain et al ). N is considered an essential element and is an constituent of many important compounds in plants (Tylova‐Munzarova et al ).…”

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“…If the over-expression of the genes from Arabidopsis thaliana involved in vitamin C synthesis and metabolism (such as AtGGP, AtGDH, AtGME, AtGPP, AtGMP and AtGalLDH), the content of vitamin C in rice grains could be significantly increased [88]. Mutations in the genes related to vitamin C synthesis and metabolism in rice will not only reduce the content of vitamin C in the grains [89], but also have an important impact on the stress resistance and the development of the whole plant in rice. Therefore, in order to solve the problem of low vitamin content in rice grains, an increase in the vitamin content of rice seeds and improved nutritional quality, rice must make full use of its genes.…”