Journal Article

Both Plant and Bacterial Nitrate Reductases Contribute to Nitric Oxide Production in Medicago truncatula Nitrogen-Fixing Nodules

Boncompagni, Eric, Prévot, Marianne, Aschi-Smiti, Samira, Horchani, Faouzi, Meilhoc, Eliane, Boscari, Alexandre, Evangelisti, Edouard, Bruand, Claude, Puppo, Alain, Raymond, Philippe, Brouquisse, Renaud

2011

Overview

Nitric oxide (NO) is a signaling and defense molecule of major importance in living organisms. In the model legume Medicago truncatula, NO production has been detected in the nitrogen fixation zone of the nodule, but the systems responsible for its synthesis are yet unknown and its role in symbiosis is far from being elucidated. In this work, using pharmacological and genetic approaches, we explored the enzymatic source of NO production in M. truncatula-Sinorhizobium meliloti nodules under normoxic and hypoxic conditions. When transferred from normoxia to hypoxia, nodule NO production was rapidly increased, indicating that NO production capacity is present in functioning nodules and may be promptly up-regulated in response to decreased oxygen availability. Contrary to roots and leaves, nodule NO production was stimulated by nitrate and nitrite and inhibited by tungstate, a nitrate reductase inhibitor. Nodules obtained with either plant nitrate reductase RNA interference double knockdown (MtNR1/2) or bacterial nitrate reductase-deficient (napA) and nitrite reductase-deficient (nirK) mutants, or both, exhibited reduced nitrate or nitrite reductase activities and NO production levels. Moreover, NO production in nodules was found to be inhibited by electron transfer chain inhibitors, and nodule energy state (ATP-ADP ratio) was significantly reduced when nodules were incubated in the presence of tungstate. Our data indicate that both plant and bacterial nitrate reductase and electron transfer chains are involved in NO synthesis. We propose the existence of a nitrate-NO respiration process in nodules that could play a role in the maintenance of the energy status required for nitrogen fixation under oxygen-limiting conditions.

• Publisher: American Society of Plant Biologists
• Subject: Agronomy. Soil science and plant productions / Anaerobic conditions / Bacteria / Bacterial Proteins / Bacterial Proteins - genetics / Bacterial Proteins - metabolism / Bacteroids / Biological and medical sciences / biosynthesis / Cell Hypoxia / Economic plant physiology / electron transport chain / energy / enzymology / Fluorescence / Fundamental and applied biological sciences. Psychology / Gene Expression Regulation, Bacterial / Gene Expression Regulation, Plant / Gene Knockdown Techniques / genetics / Hypoxia / leaves / legumes / Medicago truncatula / Medicago truncatula - enzymology / Medicago truncatula - genetics / Medicago truncatula - microbiology / metabolism / microbiology / Mitochondria / Mitochondria - enzymology / mutants / nitrate reductase / Nitrate Reductases / Nitrate Reductases - genetics / Nitrate Reductases - metabolism / Nitrates / Nitrates - pharmacology / nitric oxide / Nitric Oxide - biosynthesis / nitrites / Nitrites - pharmacology / Nitrogen Fixation / Nodules / normoxia / Oxides / Oxygen / Oxygen - physiology / Parasitism and symbiosis / pharmacology / physiology / Plant physiology and development / Plant Proteins / Plant Proteins - genetics / Plant Proteins - metabolism / Plant roots / Plants / PLANTS INTERACTING WITH OTHER ORGANISMS / RNA Interference / Root Nodules, Plant / Root Nodules, Plant - enzymology / Root Nodules, Plant - microbiology / Root Nodules, Plant - physiology / roots / Sinorhizobium meliloti / Sinorhizobium meliloti - enzymology / Sinorhizobium meliloti - genetics / Sinorhizobium meliloti - physiology / Symbiosis / Symbiosis (nodules, symbiotic nitrogen fixation, mycorrhiza...) / Tungsten Compounds / Tungsten Compounds - pharmacology