AUTHOR=Larrainzar Estíbaliz , Gil-Quintana Erena , Seminario Amaia , Arrese-Igor Cesar , González Esther M. 

TITLE=Nodule carbohydrate catabolism is enhanced in the Medicago truncatula A17-Sinorhizobium medicae WSM419 symbiosis

JOURNAL=Frontiers in Microbiology

VOLUME=5

YEAR=2014

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2014.00447

DOI=10.3389/fmicb.2014.00447

ISSN=1664-302X

ABSTRACT=<p>The symbiotic association between <italic>Medicago truncatula</italic> and <italic>Sinorhizobium meliloti</italic> is a well-established model system in the legume–<italic>Rhizobium</italic> community. Despite its wide use, the symbiotic efficiency of this model has been recently questioned and an alternative microsymbiont, <italic>S. medicae</italic>, has been proposed. However, little is known about the physiological mechanisms behind the higher symbiotic efficiency of <italic>S. medicae</italic> WSM419. In the present study, we inoculated <italic>M. truncatula</italic> Jemalong A17 with either <italic>S. medicae</italic> WSM419 or <italic>S. meliloti</italic> 2011 and compared plant growth, photosynthesis, N<sub>2</sub>-fixation rates, and plant nodule carbon and nitrogen metabolic activities in the two systems.<italic> M. truncatula</italic> plants in symbiosis with <italic>S. medicae</italic> showed increased biomass and photosynthesis rates per plant. Plants grown in symbiosis with <italic>S. medicae</italic> WSM419 also showed higher N<sub>2</sub>-fixation rates, which were correlated with a larger nodule biomass, while nodule number was similar in both systems. In terms of plant nodule metabolism, <italic>M. truncatula</italic>–<italic>S. medicae</italic> WSM419 nodules showed increased sucrose-catabolic activity, mostly associated with sucrose synthase, accompanied by a reduced starch content, whereas nitrogen-assimilation activities were comparable to those measured in nodules infected with <italic>S. meliloti</italic> 2011. Taken together, these results suggest that <italic>S. medicae</italic> WSM419 is able to enhance plant carbon catabolism in <italic>M. truncatula</italic> nodules, which allows for the maintaining of high symbiotic N<sub>2</sub>-fixation rates, better growth and improved general plant performance.</p>