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.
Highlights
The coordinated expression of the genes involved in respiration in the photosynthetic cyanobacterium Synechocystis sp
The putative genes involved in carbohydrate metabolism were identified during the sequencing of the Synechocystis genome (Yang et al, 2002; Knowles and Plaxton, 2003); biochemical evidence for the functional role of these gene products is limited to glucokinase (Lee et al, 2005), Glc-6-P dehydrogenase (G6PDH) (Scanlan et al, 1995), 6-phosphogluconate dehydrogenase (Broedel and Wolf, 1990), glyceraldehyde-3-P dehydrogenase (Koksharova et al, 1998), PK (Knowles et al, 2001), phosphoenolpyruvate kinase (PPC; Luinenburg and Coleman, 1990), FBA (Nakahara et al, 2003), and PFK (Pelroy et al, 1976)
The expression of genes coding proteins that are associated with the glycolytic and oxidative pentose phosphate (OPP) pathways has been intensively investigated under different nutrition modes (Yang et al, 2002; Knowles and Plaxton, 2003; Osanai et al, 2005; Singh and Sherman, 2005; Kahlon et al, 2006); there are very few studies relating to genes that regulate the tricarboxylic acid (TCA) cycle, respiratory electron transport, and ATP synthesis
Summary
The coordinated expression of the genes involved in respiration in the photosynthetic cyanobacterium Synechocystis sp. To examine the expression profiles of all (putative) respiratory genes during the early period of Glc feeding, genes encoding key enzymes involved in glycolysis, the OPP pathway, the Calvin cycle, glycogen and Suc metabolism, photosynthetic and respiratory electron transport, and oxidative phosphorylation were included in a DNA microarray analysis (Supplemental Table S1).
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