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Journal of Bacteriology, June 2009, p. 3992-4001, Vol. 191, No. 12
0021-9193/09/$08.00+0     doi:10.1128/JB.00132-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Simultaneous Inactivation of Sigma Factors B and D Interferes with Light Acclimation of the Cyanobacterium Synechocystis sp. Strain PCC 6803{triangledown} ,{dagger}

Maija Pollari, Virpi Ruotsalainen, Susanne Rantamäki, Esa Tyystjärvi, and Taina Tyystjärvi*

Plant Physiology and Molecular Biology, Department of Biology, University of Turku, FI-20014 Turku, Finland

Received 30 January 2009/ Accepted 27 March 2009

In cyanobacteria, gene expression is regulated mainly at the level of transcription initiation, which is mediated by the RNA polymerase holoenzyme. The RNA polymerase core is catalytically active, while the {sigma} factor recognizes promoter sequences. Group 2 {sigma} factors are similar to the principal {sigma} factor but are nonessential. Group 2 {sigma} factors SigB and SigD are structurally the most similar {sigma} factors in Synechocystis sp. strain PCC 6803. Under standard growth conditions, simultaneous inactivation of sigB and sigD genes did not affect the growth, but the photosynthesis and growth of the {Delta}sigBD strain were slower than in the control strain at double light intensity. Light-saturated electron transfer rates and the fluorescence and thermoluminescence measurements showed that photosynthetic light reactions are fully functional in the {Delta}sigBD strain, but absorption and 77 K emission spectra measurements suggest that the light-harvesting system of the {Delta}sigBD strain does not acclimate normally to higher light intensity. Furthermore, the {Delta}sigBD strain is more sensitive to photoinhibition under bright light because impaired upregulation of psbA genes leads to insufficient PSII repair.

* Corresponding author. Mailing address: Plant Physiology and Molecular Biology, Department of Biology, University of Turku, FI-20014 Turku, Finland. Phone: 358-2-3335797. Fax: 358-2-3335549. E-mail: taityy{at}utu.fi

{triangledown} Published ahead of print on 10 April 2009.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

Journal of Bacteriology, June 2009, p. 3992-4001, Vol. 191, No. 12
0021-9193/09/$08.00+0     doi:10.1128/JB.00132-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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