Department of Plant Biology, Cornell University, Ithaca, NY, USA.
Mol Plant Microbe Interact. 2011 Nov;24(11):1289-95. doi: 10.1094/MPMI-05-11-0114.
Recent refinements to the phylogeny of rosid angiosperms support the conclusion that nodulation has evolved several times in the so-called N(2)-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.
共生固氮作用在所谓的固氮类群（NFC）中多次进化，并为这些起源提供了时间。大约在 1 亿年前（MYA），发生了促使共生固氮进化的假定倾向性事件，此后迅速辐射的各个谱系保留了这种倾向性事件，并在每个共生固氮谱系中至少另外 3000 万年中保持其非固氮作用的功能。豆科植物起源后不久就迅速辐射，而共生固氮很可能在这一辐射过程中多次进化。豆目植物的主要谱系在共生固氮起源的附近分化，这解释了该类群中根瘤生物学的多样性。共生固氮共生关系体现了“深度同源”的概念，在共生固氮的非同源起源中共享各种同源成分，这主要归因于从现有功能（特别是较老的丛枝菌根共生关系）的招募。尽管多倍体可能在豆目植物根瘤的起源中发挥了作用，但在其他豆科植物中并非如此，蔷薇类的全基因组三倍体化也没有直接导致共生固氮的倾向性事件。
