Gene

Root nodule

Genome

Nitrogen fixation

Medicago truncatula

Medicago

Rhizobiaceae

Rhizobium

Symbiosis

Bacteria

Genetics

Botany

Evolutionary biology

Biology

Proceedings of the National Academy of Sciences

Significance Fixed nitrogen is essential for plant growth. Some plants, such as legumes, can host nitrogen-fixing bacteria within cells in root organs called nodules. Nodules are considered to have evolved in parallel in different lineages, but the genetic changes underlying this evolution remain unknown. Based on gene expression in the nitrogen-fixing nonlegume Parasponia andersonii and the legume Medicago truncatula , we find that nodules in these different lineages may share a single origin. Comparison of the genomes of Parasponia with those of related nonnodulating plants reveals evidence of parallel loss of genes that, in legumes, are essential for nodulation. Taken together, this raises the possibility that nodulation originated only once and was subsequently lost in many descendant lineages.

Comparative genomics of the nonlegume <i>Parasponia</i> reveals insights into evolution of nitrogen-fixing rhizobium symbioses

Comparative genomics of the nonlegume Parasponia reveals insights into evolution of nitrogen-fixing rhizobium symbioses