title: Chloroplast gene sequence data suggest a single origin of the predisposition for symbiotic nitrogen fixation in angiosperms.
abstract: Of the approximately 380 families of angiosperms, representatives of only 10 are known to form symbiotic associations with nitrogen-fixing bacteria in root nodules. The morphologically based classification schemes proposed by taxonomists suggest that many of these 10 families of plants are only distantly related, engendering the hypothesis that the capacity to fix nitrogen evolved independently several, if not many, times. This has in turn influenced attitudes toward the likelihood of transferring genes responsible for symbiotic nitrogen fixation to crop species lacking this ability. Phylogenetic analysis of DNA sequences for the chloroplast gene rbcL indicates, however, that representatives of all 10 families with nitrogen-fixing symbioses occur together, with several families lacking this association, in a single clade. This study therefore indicates that only one lineage of closely related taxa achieved the underlying genetic architecture necessary for symbiotic nitrogen fixation in root nodules.
authors.affiliation: Department of Botany, Washington State University, Pullman 99164-4238, USA.
authors.forename: D E
authors.initials: DE
authors.lastname: Soltis
authors.forename: P S
authors.initials: PS
authors.lastname: Soltis
authors.forename: D R
authors.initials: DR
authors.lastname: Morgan
authors.forename: S M
authors.initials: SM
authors.lastname: Swensen
authors.forename: B C
authors.initials: BC
authors.lastname: Mullin
authors.forename: J M
authors.initials: JM
authors.lastname: Dowd
authors.forename: P G
authors.initials: PG
authors.lastname: Martin
mesh_terms: D001483:Base Sequence; D002736:Chloroplasts / Q000378:metabolism*; D016384:Consensus Sequence; D017343:Genes, Plant; D006094:Gram-Positive Bacteria / Q000502:physiology*; D008969:Molecular Sequence Data; D009586:Nitrogen Fixation / Q000235:genetics*; D010802:Phylogeny; D010944:Plants / Q000145:classification / Q000235:genetics* / Q000382:microbiology; D012231:Rhizobium / Q000502:physiology*; D012273:Ribulose-Bisphosphate Carboxylase / Q000235:genetics*; D012689:Sequence Homology, Nucleic Acid; D013559:Symbiosis; D014197:Trees / Q000145:classification / Q000235:genetics
chemical_list: D012273:Ribulose-Bisphosphate Carboxylase