Title : Redox state components controls the nitrogenfixing symbiosis between Medicago truncatula and Sinorhizobium meliloti
The world population growth associated with the shortage of fossil resources and global climate change create a strong socioeconomic demand for the development of plant production systems requiring less natural resources and more respectful of the environment. Legume plants provide an answer to these issues, thanks to their capacity to establish a symbiotic relationship with nitrogenfixing rhizobia. In fact, legume crops have the unique ability to grow efficiently without nitrogen fertilizers, which are notorious for their negative environmental impact in terms of fossil energy consumption, greenhouse gas emission and water pollution. Nitrogen-fixing symbiosis leads to the formation of a new organ, the root nodule. Inside the plant nodule cells, the bacteria differentiate into bacteroids, able to reduce atmospheric nitrogen in ammonia which is then supplied to the plant in exchange of carbon sources. The cellular redox state regulates root nodule development and functioning. More precisely, redox signals are involved in the regulation of the early steps of the interaction, in the differentiation of the two symbiotic partners and in the efficiency of the nitrogen fixation. This presentation will address the importance of redox control through the production of reactive nitrogen and oxygen species and the presence of an efficient antioxidant defence in the two symbiotic partners. On one hand, the lecture will present the involvement of nitric oxide and hydrogen peroxide in the crosstalk between the two symbiotic partners and in the regulation of the biological nitrogen fixation during the interaction between M. truncatula and S. meliloti. On the other hand, the importance of glutathione and other molecular components of the antioxidant defence in the redox state equilibrium and the efficiency of symbiotic nitrogen fixation will also be addressed. This lecture will provide an overview of the involvement of redox equilibrium in the regulation of the symbiotic nitrogen fixation.