AUTHOR=Lamouche Florian , Bonadé-Bottino Nolwenn , Mergaert Peter , Alunni Benoit 

TITLE=Symbiotic Efficiency of Spherical and Elongated Bacteroids in the Aeschynomene-Bradyrhizobium Symbiosis

JOURNAL=Frontiers in Plant Science

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2019.00377

DOI=10.3389/fpls.2019.00377

ISSN=1664-462X

ABSTRACT=<p>The legume-rhizobium symbiosis is a major supplier of fixed nitrogen in the biosphere and constitutes a key step of the nitrogen biogeochemical cycle. In some legume species belonging to the Inverted Repeat Lacking Clade (IRLC) and the Dalbergioids, the differentiation of rhizobia into intracellular nitrogen-fixing bacteroids is terminal and involves pronounced cell enlargement and genome endoreduplication, in addition to a strong loss of viability. In the <italic>Medicago truncatula-Sinorhizobium</italic> spp. system, the extent of bacteroid differentiation correlates with the level of symbiotic efficiency. Here, we used different physiological measurements to compare the symbiotic efficiency of photosynthetic bradyrhizobia in different <italic>Aeschynomene</italic> spp. (Dalbergioids) hosts inducing different bacteroid morphotypes associated with increasing ploidy levels. The strongly differentiated spherical bacteroids were more efficient than the less strongly differentiated elongated ones, providing a higher mass gain to their hosts. However, symbiotic efficiency is not solely correlated with the extent of bacteroid differentiation especially in spherical bacteroid-inducing plants, suggesting the existence of other factors controlling symbiotic efficiency.</p>