Biosynthetic pathways of vitamin E, vitamin K1, carotenoid and plastoquinone.

<p>Substrate abbreviations: DHNA, 1,4-dihydroxy-2-naphtoate; DMPBQ, 2,3-dimethyl-5-phytyl benzoquinol; DMPQ, demethylphylloquinone; DMAPP, dimethylallyl diphosphate; GGDP, geranylgeranyl diphosphate; HGA, homogentisate; HPP, ρ-hydroxyphenylpyruvate; IPP, isopentenyl diphosphate; MPBQ, 2-methyl-6-phytyl-1,4-benzoquinol; MSBQ, 2-methyl-6-solanesyl-1,4-benzoquinol; PDP, phytyl diphosphate; SDP, solanesyl diphosphate. Enzyme abbreviations: DHNA-PT, DHNA phytyl transferase; DMPQ-MT, DMPQ methyltransferase; GGPS, geranylgeranyl diphosphate synthase; GGR, geranylgeranyl reductase; HPPD, HPP dioxygenase; HPT, homogentisate phytyl transferase; HST, homogentisate solanesyl transferase; MPBQ/MSBQ-MT, MPBQ/MSBQ methyltransferase; PSY, phytoene synthase; TC, tocopherol cyclase; γ-TMT, γ-tocopherol methyltransferase.</p

Roles of MPBQ-MT in Promoting α/γ-Tocopherol Production and Photosynthesis under High Light in Lettuce

<div><p>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 (<i>Lactuca sativa</i>) by rapid amplification of cDNA ends (RACE), named <i>LsMT</i>. Overexpression of <i>LsMT</i> 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 <i>LsMT</i> significantly increased plastoquinone (PQ) level. The increase of tocopherol and plastoquinone levels by <i>LsMT</i> 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 <i>MPBQ-MT</i> can be further explored for enhancing vitamin E value, strengthening photosynthesis and phototolerance under high light in plants.</p></div

Expression levels of genes encoding HPPD, HPT, MPBQ-MT, TC and γ-TMT involved in tocopherol biosynthesis in wild type (WT) and transgenic lines (M1-M4), measured by quantitative real-time PCR.

<p><i>Ubiquitin</i> was used as a control for normalization. mRNA expression levels (y-axis) of the five genes were measured with 2^-ΔCt. Data is the mean value ± SD of four biological replicates from T1 progenies. Asterisk indicated a significant difference compared to the value of WT (Student’s <i>t</i>-test, P<0.05).</p

Measurements of chlorophyll fluorescence, photooxidation products, NPQ level and soluble sugar content in wild type (WT) and transgenic plants’ leaves under high light condition (photon flux density: 1000μmol/m²/s, 16h light/8h dark) for 6 days.

<p>The measurements were taken after 0, 3, 6 days of the treatment. (A) the actual quantum yield of PSⅡ-mediated electron transport, (B) the maximum quantum yield of PSⅡ photochemistry, (C) H₂O₂ content, (D) malondialdehyde (MDA) content, (E) NPQ level and (F) soluble sugar content. Data is the mean value ± SD of four biological replicates from T1 progenies. Asterisk indicated a significant difference compared to the value of WT (Student’s <i>t</i>-test, P<0.05).</p

Relative plastoquinone level in wild type (WT) and transgenic lines (M1-M4).

<p>Data is the mean value ± SD of four biological replicates from T1 progenies. Asterisk indicated a significant difference compared to the value of WT (Student’s <i>t</i>-test, P<0.05).</p

Heat map derived from the drought-responsive gene co-expression network.

<p>A, heat map of our network. Genes in the rows and columns have been ordered by a MCL algorithm. Each of the colored bars along the top horizontal and left vertical axes represents a gene module. Genes that do not belong to any module are colored gray. B, heat map of the WGCNA network based on power (β = 4). The genes are colored by module assignment in A.</p

Degree distribution of the drought-responsive gene co-expression network.

<p>A, the preliminary network without the maximum connection. B, the final drought-responsive gene network.</p

Mapping the modules onto the drought-responsive gene co-expression network.

<p>The nodes are color-coded by modules and gray nodes represent genes unassigned to a module. The over-represented GO terms are shown for each module. Each pie chart represents the proportion of up- (yellow color) and downregulated (blue color) genes in the corresponding module.</p

Choosing Pearson correlation coefficient cutoff value.

<p>A, the actual number of edges and all possible edges among the non-singleton nodes as a function of correlation coefficient cutoff values. B, network density at different correlation coefficient cutoff values.</p

Tissue-specific expression of genes in the drought-responsive modules.

<p>The average expression level for each gene in different tissue types was calculated based on the normalized Affymetrix array data.</p