Abstract
2-methyl-6-phytyl-1, 4-benzoquinol methyltransferase (MPBQ-MT) is a vital enzyme catalyzing a key methylation step in both α/γ-tocopherol and plastoquinone biosynthetic pathway. In this study, the gene encoding MPBQ-MT was isolated from lettuce (Lactuca sativa) by rapid amplification of cDNA ends (RACE), named LsMT. Overexpression of LsMT in lettuce brought about a significant increase of α- and γ-tocopherol contents with a reduction of phylloquinone (vitamin K1) content, suggesting a competition for a common substrate phytyl diphosphate (PDP) between the two biosynthetic pathways. Besides, overexpression of LsMT significantly increased plastoquinone (PQ) level. The increase of tocopherol and plastoquinone levels by LsMT overexpression conduced to the improvement of plants’ tolerance and photosynthesis under high light stress, by directing excessive light energy toward photosynthetic production rather than toward generation of more photooxidative damage. These findings suggest that the role and function of MPBQ-MT can be further explored for enhancing vitamin E value, strengthening photosynthesis and phototolerance under high light in plants.
Highlights
MPBQ-MT is an important gene involved in both tocopherol and plastoquinone biosynthesis (Fig 1), which was first isolated from and characterized in Arabidopsis thaliana by screening of mutants deficient in α-/γ-tocopherol and plastoquinone [1, 2]
The coding sequence of MPBQ-MT from lettuce (LsMT) was isolated by rapid amplification of cDNA ends (RACE) and its full length was obtained by genomic DNA amplification
The result showed there is no significant difference in the expression levels of HPPD, HPT, TC and γ-TMT between wild type and transgenic plants, indicating that overexpression of LsMT does not impact on the expression of other genes up- and downstream in the tocopherol biosynthetic pathway
Summary
MPBQ-MT is an important gene involved in both tocopherol (vitamin E) and plastoquinone biosynthesis (Fig 1), which was first isolated from and characterized in Arabidopsis thaliana by screening of mutants deficient in α-/γ-tocopherol and plastoquinone [1, 2]. Quantitative PCR (qPCR) result showed the transcription level of LsMT in transgenic plants increased by 1.5–5 folds, compared to that in wild type plants (Fig 2). We analyzed the expression levels of HPPD, HPT, TC, γ-TMT, to see if the upregulation of LsMT expression in transgenic plants has any impact on the expression of these up- and downstream genes in the tocopherol biosynthetic pathway (Fig 2).
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