Abstract
The tricarboxylic acid (TCA) cycle and pyruvate metabolism of cyanobacteria are unique and important from the perspectives of biology and biotechnology research. Rre37, a response regulator induced by nitrogen depletion, activates gene expression related to sugar catabolism. Our previous microarray analysis has suggested that Rre37 controls the transcription of genes involved in sugar catabolism, pyruvate metabolism, and the TCA cycle. In this study, quantitative real-time PCR was used to measure the transcript levels of 12 TCA cycle genes and 13 pyruvate metabolism genes. The transcripts of 6 genes (acnB, icd, ppc, pyk1, me, and pta) increased after 4 h of nitrogen depletion in the wild-type GT strain but the induction was abolished by rre37 overexpression. The repression of gene expression of fumC, ddh, and ackA caused by nitrogen depletion was abolished by rre37 overexpression. The expression of me was differently affected by rre37 overexpression, compared to the other 24 genes. These results indicate that Rre37 differently controls the genes of the TCA cycle and pyruvate metabolism, implying the key reaction of the primary in this unicellular cyanobacterium.
Highlights
The tricarboxylic acid (TCA) cycle and pyruvate metabolism are conserved in almost all organisms and are indispensable for cell survival and proliferation
The transcripts of 12 genes related to the TCA cycle, gltA, acnB, icd, gabD, kgd, sucC, sucD, sdhA, sdhB, sdhB, fumC, and citH, were measured using cells grown under nitrogen-replete conditions or nitrogen-depleted conditions for 4 h
The expression of acnB and icd increased in the GT strain after 4 h of nitrogen depletion (Figure 1). rre37 overexpression abolished the induction of acnB and icd expression under nitrogendepleted conditions (Figure 1)
Summary
The tricarboxylic acid (TCA) cycle and pyruvate metabolism are conserved in almost all organisms and are indispensable for cell survival and proliferation. In this cyanobacterium, 2-OG is converted to succinic semialdehyde, a step catalyzed by a 2-OG decarboxylase, and succinic semialdehyde is converted to succinate by a succinic semialdehyde dehydrogenase [2]. 2-OG is converted to succinic semialdehyde, a step catalyzed by a 2-OG decarboxylase, and succinic semialdehyde is converted to succinate by a succinic semialdehyde dehydrogenase [2] Genes encoding these two enzymes are conserved among cyanobacteria, except in marine species, indicating that the closed TCA cycle is widely maintained in cyanobacteria. Metabolomic analyses have revealed that, in addition to 2-OG, other organic acids in the TCA cycle, including succinate, malate, and fumarate, are increased by nitrogen depletion in the unicellular cyanobacterium Synechocystis sp. The redistribution of carbon sources to various metabolites other than glycogen has been shown in the freshwater
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