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

Abstract

The coordinated expression of the genes involved in respiration in the photosynthetic cyanobacterium Synechocystis sp. PCC 6803 during the early period of glucose (Glc) treatment is poorly understood. When photoautotrophically grown cells were supplemented with 10 mM Glc in the light or after a dark adaptation period of 14 h, significant increases in the respiratory activity, as determined by NAD(P)H turnover, respiratory O 2 uptake rate, and cytosolic alkalization, were observed. At the same time, the transcript levels of 18 genes coding for enzymes associated with respiration increased with differential induction kinetics; these genes were classified into three groups based on their half-rising times. Transcript levels of the four genes gpi, zwf, pdhB, and atpB started to increase along with a net increase in NAD(P)H, while the onset of net NAD(P)H consumption coincided with an increase in those of the genes tktA, ppc, pdhD, icd, ndhD2, ndbA, ctaD1, cydA, and atpE. In contrast, the expression of the atpI/G/D/A/C genes coding for ATP synthase subunits was the slowest among respiratory genes and their expression started to accumulate only after the establishment of cytosolic alkalization. These differential effects of Glc on the transcript levels of respiratory genes were not observed by inactivation of the genes encoding the Glc transporter or glucokinase. In addition, several Glc analogs could not mimic the effects of Glc. Our findings suggest that genes encoding some enzymes involved in central carbon metabolism and oxidative phosphorylation are coordinately regulated at the transcriptional level during the switch of nutritional mode.Respiration releases the energy stored in carbon compounds and also provides many carbon precursors for the biosynthesis of a wide variety of plant biomolecules, including amino acids, lipids, isoprenoids, and porphyrins. D-Glc (hereafter Glc) is an immediate substrate for the four major respiration processes: glycolysis, the oxidative pentose phosphate (OPP) pathway, the tricarboxylic acid (TCA) cycle, and oxidative phosphorylation. In plants, respiration is predominantly controlled by the key metabolites ADP and inorganic phosphate, and the ratio of NADPH to NADP 1 . The cellular concentration of ADP initially controls the rates of electron transfer and ATP synthesis, which in turn affect TCA cycle activity, finally resulting in the regulation of glycolytic reactions.

Role of Type 2 NAD(P)H Dehydrogenase NdbC in Redox Regulation of Carbon Allocation in Synechocystis

“…The amounts of two key enzymes, Glc-6-P dehydrogenase (Zwf) and 6-phosphogluconolactonase (Gnd), specific for OPP as well as PfkA involved in EMP were likewise reduced in the DndbC mutant (Table III). These results are in agreement with earlier studies showing that the mRNA amount of ndbC follows circadian rhythm peaking in the dark together with genes involved in sugar catabolism (Kucho et al, 2005;Layana and Diambra, 2011) as well as in the beginning of heterotrophy (Lee et al, 2007). Conversely, 6-PG hydratase (IlvD), which belongs to the recently discovered Entner-Doudoroff pathway in cyanobacteria (Chen et al, 2016), was up-regulated in DndbC in LC (Table III) and might partially compensate for the down-regulation of EMP and OPP.…”

The Nitrogen-regulated Response Regulator NrrA Controls Cyanophycin Synthesis and Glycogen Catabolism in the Cyanobacterium Synechocystis sp. PCC 6803

“…In addition to nitrogen regulation by NtcA, expression of the nrrA gene in Synechocystis is enhanced by glucose and high salt (45,46). It is tempting to speculate that NrrA may also control cyanophycin accumulation and sugar catabolism under glucose and high salt conditions.…”

Impaired glycogen synthesis causes metabolic overflow reactions and affects stress responses in the cyanobacterium Synechocystis sp. PCC 6803

“…The polymer likely has a similar role during transitions of cyanobacteria to periods of nitrogen starvation or to photomixotrophic growth. Both conditions conceivably mimic the physiological states of cells under light-dark transitions (Lee et al, 2007) and will be discussed below in more detail.…”