Evolution of Symbiosis Genes: Vertical and Horizontal Gene Transfer
Conserved nitrogen fixation genes nifHDK and nifENB have been found in 14 phyla from either bacteria or archaea (Dos Santos et al. 2012), while nodulation function is restricted to Alphaproteobacteria and Betaproteobacteria. Consequently, nitrogen fixation is proposed to predate nodulation function. Although nif genes can be co-transferred with nod genes among rhizobia (Sullivan et al. 1995; Sullivan and Ronson 1998), the symbiosis-specific nif genes can have a close relationship with homologues from non-symbiotic loci or non-rhizobial strains of the same genus (Bontemps et al. 2010; Okubo et al. 2016), indicating potential replacement of transferred nif genes by indigenous ones. Moreover, the flavonoid-induced transfer of a symbiosis island harbouring nod but not nif genes from Azorhizobium caulinodans to other rhizobia has been reported (Ling et al. 2016). Therefore, the evolutionary history of nitrogen fixation genes can be disassociated from that of nodulation genes (Fig. 6.1).
- Barcellos FG, Menna P, Batista JSD, et al. Evidence of horizontal transfer of symbiotic genes from a Bradyrhizobium japonicum inoculant strain to indigenous diazotrophs Sinorhizobium (Ensifer) fredii and Bradyrhizobium elkanii in a Brazilian Savannah soil. Appl Environ Microbiol. 2007;73:2635–43. https://doi.org/10.1128/Aem.01823-06.CrossRefPubMedPubMedCentralGoogle Scholar
- Capela D, Marchetti M, Clérissi C, et al. Recruitment of a lineage-specific virulence regulatory pathway promotes intracellular infection by a plant pathogen experimentally evolved into a legume symbiont. Mol Biol Evol. 2017;34:2503–21. https://doi.org/10.1093/molbev/msx165.CrossRefPubMedGoogle Scholar
- Ktari A, Nouioui I, Furnholm T, et al. Permanent draft genome sequence of Frankia sp. NRRL B-16219 reveals the presence of canonical nod genes, which are highly homologous to those detected in Candidatus Frankia Dg1 genome. Stand Genomic Sci. 2017;12:1–10. https://doi.org/10.1186/s40793-017-0261-3.CrossRefGoogle Scholar
- Persson T, Battenberg K, Demina IV, et al. Candidatus Frankia datiscae Dg1, the Actinobacterial microsymbiont of Datisca glomerata, expresses the canonical nod genes nodABC in symbiosis with its host plant. PLoS One. 2015;10:e0127630. https://doi.org/10.1371/journal.pone.0127630.CrossRefPubMedPubMedCentralGoogle Scholar
- Zhang XX, Guo HJ, Wang R, et al. Genetic divergence of Bradyrhizobium nodulating soybeans as revealed by multilocus sequence analysis of genes inside and outside the symbiosis island. Appl Environ Microbiol. 2014;80:3181–90. https://doi.org/10.1128/AEM.00044-14.CrossRefPubMedPubMedCentralGoogle Scholar