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

Klotz A, Reinhold E, Doello S, Forchhammer K - Life (Basel) (2015)

Bottom Line: This study established a method that allows uncoupling metabolic and redox-signals involved in nitrogen-starvation acclimation.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 Article: PubMed Central - PubMed

Affiliation: Interfakultäres Institut für Mikrobiologie und Infektionsmedizin der Eberhard-Karls-Universität Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany. alexander.klotz@uni-tuebingen.de.

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.

No MeSH data available.


Related in: MedlinePlus

Effect of nitrate and nitrite compared to ammonia on MSX-induced nblA::luxAB or glnB::luxAB expression. (A) nblA::luxAB expression of WT-C 103 cells growing in media with different nitrogen sources within 5 h after MSX treatment (2 µM): 17.7 mM nitrate, 5 mM nitrite and 5 mM ammonia. (B) Highlighting of the results of nblA::luxAB expression of WT-C 103 in nitrate (17.7 mM) or nitrite (5 mM) containing media. (C) glnB::luxAB expression of FAM2 cells in media with nitrate (17.7 mM) and ammonia (5 mM) within 5 h after MSX treatment (2 µM).
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life-05-00888-f005: Effect of nitrate and nitrite compared to ammonia on MSX-induced nblA::luxAB or glnB::luxAB expression. (A) nblA::luxAB expression of WT-C 103 cells growing in media with different nitrogen sources within 5 h after MSX treatment (2 µM): 17.7 mM nitrate, 5 mM nitrite and 5 mM ammonia. (B) Highlighting of the results of nblA::luxAB expression of WT-C 103 in nitrate (17.7 mM) or nitrite (5 mM) containing media. (C) glnB::luxAB expression of FAM2 cells in media with nitrate (17.7 mM) and ammonia (5 mM) within 5 h after MSX treatment (2 µM).

Mentions: As shown in Figure 5A, both, nitrate and nitrite almost completely prevented MSX-induced nblA expression. A detailed zoom into the reporter activity of nitrate- and nitrite-incubated cells showed that the inhibitory effect of nitrate is slightly stronger than that of nitrite indicated in Figure 5B. By comparison, with a reduction to about one third, nitrate did not that strongly supress the induction of the purely NtcA-dependent glnB promoter in the FAM-2 reporter (Figure 5C).


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

Klotz A, Reinhold E, Doello S, Forchhammer K - Life (Basel) (2015)

Effect of nitrate and nitrite compared to ammonia on MSX-induced nblA::luxAB or glnB::luxAB expression. (A) nblA::luxAB expression of WT-C 103 cells growing in media with different nitrogen sources within 5 h after MSX treatment (2 µM): 17.7 mM nitrate, 5 mM nitrite and 5 mM ammonia. (B) Highlighting of the results of nblA::luxAB expression of WT-C 103 in nitrate (17.7 mM) or nitrite (5 mM) containing media. (C) glnB::luxAB expression of FAM2 cells in media with nitrate (17.7 mM) and ammonia (5 mM) within 5 h after MSX treatment (2 µM).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4390884&req=5

life-05-00888-f005: Effect of nitrate and nitrite compared to ammonia on MSX-induced nblA::luxAB or glnB::luxAB expression. (A) nblA::luxAB expression of WT-C 103 cells growing in media with different nitrogen sources within 5 h after MSX treatment (2 µM): 17.7 mM nitrate, 5 mM nitrite and 5 mM ammonia. (B) Highlighting of the results of nblA::luxAB expression of WT-C 103 in nitrate (17.7 mM) or nitrite (5 mM) containing media. (C) glnB::luxAB expression of FAM2 cells in media with nitrate (17.7 mM) and ammonia (5 mM) within 5 h after MSX treatment (2 µM).
Mentions: As shown in Figure 5A, both, nitrate and nitrite almost completely prevented MSX-induced nblA expression. A detailed zoom into the reporter activity of nitrate- and nitrite-incubated cells showed that the inhibitory effect of nitrate is slightly stronger than that of nitrite indicated in Figure 5B. By comparison, with a reduction to about one third, nitrate did not that strongly supress the induction of the purely NtcA-dependent glnB promoter in the FAM-2 reporter (Figure 5C).

Bottom Line: This study established a method that allows uncoupling metabolic and redox-signals involved in nitrogen-starvation acclimation.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 Article: PubMed Central - PubMed

Affiliation: Interfakultäres Institut für Mikrobiologie und Infektionsmedizin der Eberhard-Karls-Universität Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany. alexander.klotz@uni-tuebingen.de.

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.

No MeSH data available.


Related in: MedlinePlus