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Life 2015, 5(1), 888-904; doi:10.3390/life5010888

Nitrogen Starvation Acclimation in Synechococcus elongatus: Redox-Control and the Role of Nitrate Reduction as an Electron Sink

1
Interfakultäres Institut für Mikrobiologie und Infektionsmedizin der Eberhard-Karls-Universität Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany
2
Department of Molecular Biosciences and Bioengineering, University of Hawaii at Manoa, Honolulu, 96822 HI, USA
These authors contributed equally to this work.
*
Author to whom correspondence should be addressed.
Academic Editors: John C. Meeks and Robert Haselkorn
Received: 8 December 2014 / Revised: 4 March 2015 / Accepted: 6 March 2015 / Published: 13 March 2015
(This article belongs to the Special Issue Cyanobacteria: Ecology, Physiology and Genetics)
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Abstract

Nitrogen starvation acclimation in non-diazotrophic cyanobacteria is characterized by a process termed chlorosis, where the light harvesting pigments are degraded and the cells gradually tune down photosynthetic and metabolic activities. The chlorosis response is governed by a complex and poorly understood regulatory network, which converges at the expression of the nblA gene, the triggering factor for phycobiliprotein degradation. This study established a method that allows uncoupling metabolic and redox-signals involved in nitrogen-starvation acclimation. Inhibition of glutamine synthetase (GS) by a precise dosage of l-methionine-sulfoximine (MSX) mimics the metabolic situation of nitrogen starvation. Addition of nitrate to such MSX-inhibited cells eliminates the associated redox-stress by enabling electron flow towards nitrate/nitrite reduction and thereby, prevents the induction of nblA expression and the associated chlorosis response. This study demonstrates that nitrogen starvation is perceived not only through metabolic signals, but requires a redox signal indicating over-reduction of PSI-reduced electron acceptors. It further establishes a cryptic role of nitrate/nitrite reductases as electron sinks to balance conditions of over-reduction. View Full-Text
Keywords: Synechococcus elongatus PCC 7942; nblA; glnB; NtcA; nitrogen starvation response; l-methionine-sulfoximine; glutamine synthetase Synechococcus elongatus PCC 7942; nblA; glnB; NtcA; nitrogen starvation response; l-methionine-sulfoximine; glutamine synthetase
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Klotz, A.; Reinhold, E.; Doello, S.; Forchhammer, K. Nitrogen Starvation Acclimation in Synechococcus elongatus: Redox-Control and the Role of Nitrate Reduction as an Electron Sink. Life 2015, 5, 888-904.

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