Abstract
The expression of carotenoid biosynthesis genes coding for phytoene synthase (crtB), phytoene desaturase (crtP), zeta-carotene desaturase (crtQ), and beta-carotene hydroxylase (crtR) is dependent upon light in the cyanobacterium Synechocystis sp. PCC 6803 (Synechocystis). We have demonstrated that the expression of the above four genes was also elevated in the dark-adapted Synechocystis cells upon glucose treatment as a consequence of transcriptional activation. Treatment with glucose analogs such as l-glucose, 3-O-methylglucose, 2-deoxyglucose, and mannose, or inactivation of glucose uptake and phosphorylation by deletion mutation of glucose transporter (glcP) and glucokinase (gk), respectively, did not induce up-regulation of carotenoid genes. When respiratory electron transport or coupling to oxidative phosphorylation was inhibited, glucose induction was not observed, indicating that respiratory electron transport per se is not critical for the expression of these genes. In agreement with this view, the extent of gene expression showed a saturation curve with increasing acridine yellow fluorescence yield, without having a close correlation with the ATP contents or ATP/ADP ratio. The results indicate that glucose induction of carotenoid gene expressions is mediated by an increase in cytosolic pH rather than either redox or glucose sensing.
Highlights
The expression of carotenoid biosynthesis genes coding for phytoene synthase, phytoene desaturase, -carotene desaturase, and -carotene hydroxylase is dependent upon light in the cyanobacterium Synechocystis sp
To determine the extent of light regulation of the key carotenoid biosynthesis genes, crtO, crtQ, and carotene hydroxylase (crtR) were analyzed in addition to crtB and crtP
To address whether redox status of electron transport is sufficient to induce gene expression, cells were exposed to glucose under dark conditions to exclude any involvement of photoreceptor systems
Summary
One microgram of total RNA was used for each reverse transcription in a 20-l reaction volume, and 0.8 l of the reaction mixture was subjected to PCR amplification in an MJ Research Minicycler under the following conditions: initial denaturation at 95 °C for 3 min, followed by 25 (crtB, crtP, and crtQ), 28 (crtR), and 8 (rRNA) cycles of 95 °C for 30 S, 60 °C for 20 S, and 72 °C for 30 S, and a final extension step at 72 °C for 7 min These RNA concentrations were within the linear response range of the PCR amplification (data not shown). The concentration of acridine yellow was 5 M and that of chlorophyll was 80 g
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