A role for the signal transduction protein P_II in the control of nitrate/nitrite uptake in a cyanobacterium

Abstract

In the cyanobacterium Synechococcus sp. strain PCC 7942, ammonium exerts a rapid and reversible inhibition of the nitrate and nitrite uptake, and the P ss protein (GlnB) is differentially phosphorylated depending on the intracellular N/C balance. RNA/DNA hybridizations, as well as nitrate and nitrite uptake experiments, were carried out with the wild-type strain and a P ss -null mutant. The transcriptional control by ammonium of the expression of the nir-nrtABCD-narB operon remained operative in the mutant but, in contrast to the wild-type strain, the mutant took up nitrate and nitrite even in the presence of ammonium. Moreover, the wild-type phenotype was restored by insertion of a copy of the wild-type glnB gene in the genome of the P ss -null mutant. These results indicate that the unphosphorylated form of P ss is involved in the short-term inhibition by ammonium of the nitrate and nitrite uptake in Synechococcus sp. strain PCC 7942.z 1998 Federation of European Biochemical Societies.

O2-dependent large electron flow functioned as an electron sink, replacing the steady-state electron flux in photosynthesis in the cyanobacterium Synechocystis sp. PCC 6803, but not in the cyanobacterium Synechococcus sp. PCC 7942

“…Cells at an arbitrary stage of growth (OD 750 = 1.5-3.0) were harvested at 7 h in the dark by centrifugation at 10,000× g for 7 min and resuspended in fresh medium. Chl a in the cyanobacteria was determined by methods reported by de Marsac and Houmard 23) .…”

Nitrate Transport and Not Photoinhibition Limits Growth of the Freshwater Cyanobacterium Synechococcus Species PCC 6301 at Low Temperature1

“…These studies also showed that the addition of l-Met sulfoximine is essential to obtain the maximal rate of nitrate consumption, which reflects the total capacity for nitrate assimilation by whole cells at a given temperature, and clearly showed that the cessation of nitrate assimilation at 15°C does not arise from the regulation of the nitrate transporter through signal transduction mediated by the P II protein (Lee at al., 1998 Hattori (1962), Synechococcus sp. PCC 6301 cells require more light to saturate, and have much greater inherent capacities for, photosynthetic oxygen evolution and carbon assimilation than for nitrate assimilation.…”

Interpreting the Plastid Carbon, Nitrogen, and Energy Status. A Role for PII?

“…PII-null mutant studies indicate a function linked to N uptake. In an ammonium regime, dephospho-PII controls the inhibition of nitrate and nitrite uptake, whereas in the absence of ammonium, it is thought that the liganded (2-oxoglutarate being the likely effector), phosphorylated PII alleviates this inhibition (Lee et al, 1998(Lee et al, , 2000. Furthermore, a PII-null mutant demonstrated that the high-affinity bicarbonate transport system of Synechocystis PCC 6803 is under PII control (Hisbergues et al, 1999).…”