Differential effects of combined N sources on early steps of the Nod factor-dependent transduction pathway in Lotus japonicus.
The development of nitrogen-fixing nodules in legumes is induced by perception of lipochitin-oligosaccharide signals secreted by a bacterial symbiont. Nitrogen (N) starvation is a prerequisite for the formation, development, and function of root nodules, and high levels of combined N in the form of nitrate or ammonium can completely abolish nodule formation. We distinguished between nitrate and ammonium inhibitory effects by identifying when and where these combined N sources interfere with the Nod-factor-induced pathway. Furthermore, we present a small-scale analysis of the expression profile, under different N conditions, of recently identified genes involved in the Nod-factor-induced pathway. In the presence of high levels of nitrate or ammonium, the NIN gene fails to be induced 24 h after the addition of Nod factor compared with plants grown under N-free conditions. This induction is restored in the hypernodulating nitrate-tolerant har1-3 mutant only in the presence of 10 and 20 mM KNO3. These results were confirmed in Lotus plants inoculated with Mesorhizobium loti. NIN plays a key role in the nodule organogenesis program and its downregulation may represent a crucial event in the nitrate-dependent pathway leading to the inhibition of nodule organogenesis.
Barbulova
Ani
A
Institute of Genetics and Biophysics A, Buzzati Traverso, Via P. Castellino 111, 80131 Napoli, Italy.
Rogato
Alessandra
A
D'Apuzzo
Enrica
E
Omrane
Selim
S
Chiurazzi
Maurizio
M
D020561:Alphaproteobacteria / Q000502:physiology; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000494:pharmacology*; D000070116:Lotus / Q000254:growth & development / Q000378:metabolism / Q000382:microbiology*; D009154:Mutation; D009566:Nitrates / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D009586:Nitrogen Fixation; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D053204:Root Nodules, Plant / Q000254:growth & development / Q000378:metabolism / Q000382:microbiology; D015398:Signal Transduction / Q000502:physiology*
D001426:Bacterial Proteins; D008070:Lipopolysaccharides; D009566:Nitrates; D000644:Quaternary Ammonium Compounds; D009584:Nitrogen