Comparison of Nodule Endophyte Composition, Diversity, and Gene Content Between Medicago truncatula Genotypes

Leguminous plants form symbiotic relationships with rhizobia. These nitrogen-fixing bacteria live in specialized root organs called nodules. Although rhizobia form the most notable host relationship within root nodules, other bacterial endophytes also inhabit nodules and can influence host–rhizobia interactions as well as exert effects of their own. In this study, we elucidate the effect of intraspecific host genetic variation and between generational legacies on root nodule endophyte communities in Medicago truncatula. Although the diversity of endophytes in nodules was similar across hosts, both nodule endophyte composition and gene functional groups differed. In contrast, neither the presence nor identity of a host in the previous generation (either A17 or R108) had a significant effect on the nodule endophyte diversity or composition. However, whether or not a host was present significantly altered gene functional groups. We conclude that genetic variation within a legume host species can play both direct and indirect effects on establishment of nodule microbiomes. Further studies, including genome-wide association studies and functional assays, can open the door for engineering and optimizing nodule endophyte communities that promote growth or have other beneficial qualities.