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Phylogenetic Perspectives on the Origins of Nodulation

November 2011 , Volume 24 , Number  11
Pages  1,289 - 1,295

Jeff J. Doyle

Department of Plant Biology, 412 Mann Library Building, Cornell University, Ithaca, NY 14853, U.S.A.

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Accepted 21 June 2011.

Recent refinements to the phylogeny of rosid angiosperms support the conclusion that nodulation has evolved several times in the so-called N2-fixing clade (NFC), and provide dates for these origins. The hypothesized predisposition that enabled the evolution of nodulation occurred approximately 100 million years ago (MYA), was retained in the various lineages that radiated rapidly shortly thereafter, and was functional in its non-nodulation role for at least an additional 30 million years in each nodulating lineage. Legumes radiated rapidly shortly after their origin approximately 60 MYA, and nodulation most likely evolved several times during this radiation. The major lineages of papilionoid legumes diverged close to the time of origin of nodulation, accounting for the diversity of nodule biology in the group. Nodulation symbioses exemplify the concept of “deep homology,” sharing various homologous components across nonhomologous origins of nodulation, largely due to recruitment from existing functions, notably the older arbuscular mycorrhizal symbiosis. Although polyploidy may have played a role in the origin of papilionoid legume nodules, it did not do so in other legumes, nor did the prerosid whole-genome triplication lead directly to the predisposition of nodulation.

© 2011 The American Phytopathological Society