Nonmetabolizable analogue of 2-oxoglutarate elicits heterocyst differentiation under repressive conditions in Anabaena sp. PCC 7120.
In response to combined nitrogen starvation in the growth medium, the filamentous cyanobacterium Anabaena sp. PCC 7120 is able to develop a particular cell type, called a heterocyst, specialized in molecular nitrogen fixation. Heterocysts are regularly intercalated among vegetative cells and represent 5-10% of all cells along each filament. In unicellular cyanobacteria, the key Krebs cycle intermediate, 2-oxoglutarate (2-OG), has been suggested as a nitrogen status signal, but in vivo evidence is still lacking. In this study we show that nitrogen starvation causes 2-OG to accumulate transiently within cells of Anabaena PCC 7120, reaching a maximal intracellular concentration of approximately 0.1 mM 1 h after combined nitrogen starvation. A nonmetabolizable fluorinated 2-OG derivative, 2,2-difluoropentanedioic acid (DFPA), was synthesized and used to demonstrate the signaling function of 2-OG in vivo. DFPA is shown to be a structural analogue of 2-OG and the process of its uptake and accumulation in vivo can be followed by (19)F magic angle spinning NMR because of the presence of the fluorine atom and its chemical stability. DFPA at a threshold concentration of 0.3 mM triggers heterocyst differentiation under repressing conditions. The multidisciplinary approaches using synthetic fluorinated analogues, magic angle spinning NMR for their analysis in vivo, and techniques of molecular biology provide a powerful means to identify the nature of the signals that remain unknown or poorly defined in many signaling pathways.
Laurent
Sophie
S
Laboratoire de Chimie Bactérienne, UPR9043, Centre National de la Recherche Scientifique, 31 Chemin Joseph Aiguier, 13402 Marseille Cedex 20, France.
Chen
Han
H
Bédu
Sylvie
S
Ziarelli
Fabio
F
Peng
Ling
L
Zhang
Cheng-Cai
CC
D017033:Anabaena / Q000166:cytology* / Q000378:metabolism*; D017931:DNA Primers; D005462:Fluorine Radioisotopes; D007656:Ketoglutaric Acids / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism*; D019906:Nuclear Magnetic Resonance, Biomolecular; D016133:Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology*
D017931:DNA Primers; D005462:Fluorine Radioisotopes; D007656:Ketoglutaric Acids; D009584:Nitrogen