Transcriptional regulation of the CO2-concentrating mechanism in a euryhaline, coastal marine cyanobacterium, Synechococcus sp. Strain PCC 7002: role of NdhR/CcmR.
Cyanobacterial photosynthesis occurs in radically diverse habitats and utilizes various forms of a CO(2)-concentrating mechanism (CCM) featuring multiple inorganic carbon (C(i)) transporters. Cyanobacteria from dynamic environments can transform CCM activity depending on C(i) availability, and yet the molecular basis for this regulation is unclear, especially in coastal strains. LysR family transcription factors resembling the Calvin cycle regulator CbbR from proteobacteria have been implicated in the expression of C(i) transporter genes in freshwater cyanobacteria. Our survey of related factors revealed a group of divergent CbbR-like sequences confined to freshwater and coastal or offshore cyanobacteria. Inactivation of the single gene (termed ccmR) from this variable cluster in the euryhaline (coastal) strain Synechococcus sp. strain PCC 7002 led to constitutive expression of a high-affinity CCM. Derepression of HCO(3)(-) transporter gene transcription, including that of BicA, a recently discovered HCO(3)(-) transporter (G. D. Price et al., Proc. Natl. Acad. Sci. USA 101:18228-18233, 2004), was observed. A unique CcmR-regulated operon containing bicA plus 9 open reading frames encoding likely Na(+)/H(+) antiporters from the CPA1 and Mnh families was defined that is essential for maximal HCO(3)(-)-dependent oxygen evolution. The promoter region required for C(i)-regulated transcription of this operon was defined. We propose that CcmR (and its associated regulon) represents a specialization for species inhabiting environments subject to fluctuating C(i) concentrations.
Woodger
Fiona J
FJ
Molecular Plant Physiology Group, Research School of Biological Sciences, Australian National University, P.O. Box 475, Canberra, ACT 0200, Australia.
Bryant
Donald A
DA
Price
G Dean
GD
D001426:Bacterial Proteins / Q000235:genetics; D001483:Base Sequence; D002245:Carbon Dioxide / Q000378:metabolism*; D002352:Carrier Proteins / Q000096:biosynthesis / Q000235:genetics; D019295:Computational Biology; D004269:DNA, Bacterial / Q000235:genetics; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D005810:Multigene Family; D009876:Operon; D010802:Phylogeny; D011401:Promoter Regions, Genetic; D012329:RNA, Bacterial / Q000096:biosynthesis; D012333:RNA, Messenger / Q000096:biosynthesis; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics; D046940:Synechococcus / Q000235:genetics* / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics; D014158:Transcription, Genetic
D001426:Bacterial Proteins; D002352:Carrier Proteins; D004269:DNA, Bacterial; D012329:RNA, Bacterial; D012333:RNA, Messenger; D017923:Sodium-Hydrogen Exchangers; D014157:Transcription Factors; D002245:Carbon Dioxide