Manipulation of the Rice L-Galactose Pathway: Evaluation of the Effects of Transgene Overexpression on Ascorbate Accumulation and Abiotic Stress Tolerance

Abstract

Ascorbic acid (AsA) is the most abundant water-soluble antioxidant in plants, and it plays a crucial role in plant growth, development and abiotic stress tolerance. In the present study, six key Arabidopsis or rapeseed genes involved in AsA biosynthesis were constitutively overexpressed in an elite Japonica rice cultivar. These genes encoded the GDP-mannose pyrophosphorylase (GMP), GDP-mannose-3',5'-epimerase (GME), GDP-L-galactose phosphorylase (GGP), L-galactose-1-phosphate phosphatase (GPP), L-galactose dehydrogenase (GDH), and L-galactono-1,4-lactone dehydrogenase (GalLDH). The effects of transgene expression on rice leaf AsA accumulation were carefully evaluated. In homozygous transgenic seedlings, AtGGP transgenic lines had the highest AsA contents (2.55-fold greater than the empty vector transgenic control), followed by the AtGME and AtGDH transgenic lines. Moreover, with the exception of the AtGPP lines, the increased AsA content also provoked an increase in the redox state (AsA/DHA ratio). To evaluate salt tolerance, AtGGP and AtGME transgenic seedlings were exposed to salt stress for one week. The relative plant height, root length and fresh weight growth rates were significantly higher for the transgenic lines compared with the control plants. Altogether, our results suggest that GGP may be a key rate-limiting step in rice AsA biosynthesis, and the plants with elevated AsA contents demonstrated enhanced tolerance for salt stress.

Knocking Down the Expression of GMPase Gene OsVTC1-1 Decreases Salt Tolerance of Rice at Seedling and Reproductive Stages

“…Studies have demonstrated that the synthesis of AsA plays important roles in the response of plants to salt stress [25, 38–40]. To further analyze the role of AsA in OsVTC1-1 -mediated enhancement of salt tolerance in rice, we examined the effect of AsA on salt tolerance of OsVTC1-1 RI seedlings with supplying exogenous AsA.…”

Medicine is not health care, food is health care: plant metabolic engineering, diet and human health

“…AtMYB12 is structurally related to the P1 regulator of flavone and phlobaphene biosynthesis in maize (Luo et al ., ). The high concentrations of flavonols produced in fruit were the consequence of AtMYB12 being able to activate expression of genes encoding enzymes of primary and intermediary metabolism, as well as those involved in flavonol metabolism (Zhang et al ., ,b). The ability of AtMYB12 to supply additional carbon skeletons, energy and reducing power for flavonoid biosynthesis, means that this TF can be used to enhance flavonoid production using a ‘push’ strategy.…”

“…The ability of AtMYB12 to supply additional carbon skeletons, energy and reducing power for flavonoid biosynthesis, means that this TF can be used to enhance flavonoid production using a ‘push’ strategy. Thus, coexpression of AtMYB12 with Delila and Rosea 1 in tomato resulted in three‐fold higher concentrations of flavonols (120 mg g −1 DW) compared to tomatoes expressing AtMYB12 alone (40 mg g −1 DW), and almost double the concentrations of anthocyanins (5.8 mg g −1 DW) compared to fruit expressing Delila and Rosea1 (3.0 mg g −1 DW; Zhang et al ., ,b). Similarly, expression of AtMYB12 together with isoflavone synthase (IFS) for the synthesis of genistin in tomato, elevated the concentrations achievable in fruit from 1.6 μg g −1 DW (with IFS alone) to c .…”

“…Similarly, expression of AtMYB12 together with isoflavone synthase (IFS) for the synthesis of genistin in tomato, elevated the concentrations achievable in fruit from 1.6 μg g −1 DW (with IFS alone) to c . 15 mg g −1 DW (for IFS plus AtMYB12) (Shih et al .,; Zhang et al ., ,b). Concentrations of genistin could be enhanced further in tomato fruit by blocking the flow of flavonoid intermediates to flavonols by introducing a mutation in the gene encoding flavanone 3‐hydroxylase, resulting in genistin concentrations of up to 80 mg g −1 DW.…”

“…Concentrations of genistin could be enhanced further in tomato fruit by blocking the flow of flavonoid intermediates to flavonols by introducing a mutation in the gene encoding flavanone 3‐hydroxylase, resulting in genistin concentrations of up to 80 mg g −1 DW. These concentrations of isoflavones are 100‐fold greater than those in soya products such as tofu (Zhang et al ., ,b). The power of incorporating a regulator that can improve the supply of not only carbon in the form of phenylalanine precursors, but also energy and reducing power from primary metabolism (glycolysis, the TCA cycle and the oxidative pentose phosphate pathway), was also demonstrated for the production of resveratrol in tomato, the concentrations of stilbenoids in fruit rising from 0.5 mg g −1 DW (with grape stilbene synthase gene alone) to 5–6 mg g −1 DW when fruit‐specific expression of AtMYB12 was combined with the expression of the gene encoding stilbene synthase from grape (Ingrosso et al ., ; Zhang et al ., ,b).…”