Send to

Choose Destination
Mol Gen Genet. 1993 Sep;240(3):435-44.

Genes at different regulatory levels are required for the ammonia control of nodulation in Rhizobium meliloti.

Author information

Institute of Genetics, Biological Research Center of Hungarian Academy of Sciences, Szeged.


The expression of the nodulation genes nodABC of Rhizobium meliloti, which determine early response functions to plant host signals, is regulated by the level of ammonia, the primary product of symbiotic nitrogen fixation. We show that the pathway that links the ammonia-induced signal to the transcriptional control of the nodABC genes involves at least two regulatory levels. The fluctuating nitrogen level is sensed and the signal is mediated by the members of the general nitrogen regulatory (ntr) system, then transmitted to the syrM-nodD3 genes representing the nod-specific level of ammonia regulation. At low ammonia concentration, the activator protein NtrC exerts its effect via nodD3. In conditions of nitrogen excess ntrR, involved in the repression of nod genes, may function in coordination with the syrM gene. Finally, the NodD3 protein may relay the nitrogen status signal to the transcriptional control of the nodABC genes.

[Indexed for MEDLINE]

Supplemental Content

Loading ...
Support Center