Glucose-induced Expression of Carotenoid Biosynthesis Genes in the Dark Is Mediated by Cytosolic pH in the Cyanobacterium Synechocystis sp. PCC 6803

Abstract

The expression of carotenoid biosynthesis genes coding for phytoene synthase (crtB), phytoene desaturase (crtP), -carotene desaturase (crtQ), and ␤-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.Carotenoids in all photosynthetic organisms including cyanobacteria participate in the light-harvesting process and function in the protection of the photosynthetic apparatus against photo-oxidative damage (1). The cyanobacterium Synechocystis sp. PCC 6803 (hereafter called Synechocystis) contains several genes encoding enzymes involved in carotenoid biosynthesis (2): the crtB gene for phytoene synthase, crtP for phytoene desaturase, crtQ for -carotene desaturase, crtO for ␤-carotene ketolase, and crtR for ␤-carotene hydroxylase.1 Despite an abundance of information about the carotenoid biosynthesis pathway and the genes involved, very little is known about the regulation of the expression of carotenoid biosynthesis genes (3).Light seems to play an important role in the expression of carotenoid biosynthesis genes. In higher plants and green algae, photoreceptors like phytochrome (4, 5) and blue light receptors (6) are involved in light signaling. But, in the cyanobacteria, redox-sensing and signaling by photosynthetic electron transport (7,8) are probably more important than other photosensory systems. This is because the content of carotenoids in Synechococcus sp. PCC 7942 is proportional to the photosynthetic rate (9), and the expression of phytoene synthase (crtB) and phytoene desaturase (crtP) genes in Synechocystis depends upon light intensity (10).To address the redox control over carotenogenesis genes, we took advantage of Synechocystis that grows at the expense of an exogenously supplied sole carbon source, glucose (11). Synechocystis cells uptake external glucose by means of a glucose transporter (glcP, the gene locus sll0771; Ref. 12) and metabolize it further via glycolys...

Sugar-Hormone Cross-Talk in Anthocyanin Biosynthesis

“…In addition to their role as energy sources, sugars are important signaling molecules involved in the growth and development of higher plants (Finkelstein and Gibson, 2002;Smeekens, 2000), and their signaling pathways have been studied extensively in free-living microorganisms such as cyanobacteria (Lee et al, 2007;Ryu et al, 2004;, bacteria (Stulke and Hillen, 1999), and yeast (Rolland et al, 2006). In Arabidopsis, anthocyanin production in cotyledons or leaves increases when seedlings are grown in a sugar-containing medium (Mita et al, 1997;Ohto et al, 2001).…”

Transcriptional Regulation of the Respiratory Genes in the CyanobacteriumSynechocystissp. PCC 6803 during the Early Response to Glucose Feeding

“…whether gene induction was mediated by Glc per se or by its phosphorylation or further metabolism, dark-adapted wild-type cells were incubated with the Glc analogs L-Glc (LGlc), 3-O-methyl-Glc (OMG), 2-deoxy-Glc (2dGlc), and Man in the dark for 1 h as reported previously for Synechocystis (Ryu et al, 2004;Lee et al, 2005).…”

“…Glc treatment induces changes in cytosolic and membrane redox states, cellular energy charge (ATP to ADP ratio), and cytosolic pH, which affect metabolism and hormone signaling, and mediates Glc repression of yeast genes (Rolland et al, 2002) and Glc induction of cyanobacterial genes (Alfonso et al, 2000;Kujat and Owttrim, 2000;Li and Sherman, 2000;Ryu et al, 2004). To see if Glc induction of respiratory gene expression is also mediated by these changes, we investigated the expression levels of 18 genes in wildtype cells treated with chemical inhibitors of the OPP pathway and oxidative phosphorylation, such as 6-aminonicotinamide (6-AN, G6PDH inhibitor; Varnes, 1988), Hg 21 (NDH-1 inhibitor; Mi et al, 1992), CN 2 (CtaI inhibitor), and carbonylcyanide-3-chlorophenyl hydrazone (CCCP; an uncoupler; Schmetterer, 1994).…”

“…PCC 6803 (hereafter Synechocystis), Glc derived from glycogen or supplied exogenously is catabolized via the OPP pathway, the lower energy-conserving phase of glycolysis, and an incomplete TCA cycle (Stal and Moezelaar, 1997). Synechocystis cells that are grown under photoautotrophic conditions and supplemented with Glc in the media show many changes in growth and carbon metabolism (Yang et al, 2002;Knowles and Plaxton, 2003;Lee et al, 2005;Osanai et al, 2005;Singh and Sherman, 2005), as well as photosynthesis and respiration (Ryu et al, 2004;Lee et al, 2005;Kurian et al, 2006), compared to cells grown in the same conditions with no Glc treatment.…”

Sugar-based growth, astaxanthin accumulation and carotenogenic transcription of heterotrophic Chlorella zofingiensis (Chlorophyta)

“…Glucose was reported to induce expression of carotenogenic genes in the cyanobacterium Synecocystis sp. PCC 6803 [23]. The glucose effects on the expression of genes are suggested to result from the glucosesensing and signaling with the hexokinase as the key sensor in a variety of yeasts, mammals and higher plants [24][25][26][27], or from changes in the cytosolic redox state or electron flow of respiratory electron transport [24,28,29].…”