title: Effect of Naturally Occurring nif Reiterations on Symbiotic Effectiveness in Rhizobium phaseoli.
abstract: Most naturally occurring strains of Rhizobium phaseoli possess reiteration of the nif genes. Three regions contain nitrogenase structural genes in strain CFN42. Two of these regions (a and b) have copies of nifH, nifD, and nifK, whereas the third region (c) contains only nifH. Strains containing mutations in either nif region a or nif region b had significantly diminished symbiotic effectiveness compared with the wild-type strain on the basis of nodule mass, total nitrogenase activity per plant, nitrogenase specific activity, total nitrogen in the shoot, and percentage of nitrogen. A strain containing mutations in both nif region a and nif region b was totally ineffective. These data indicate that both nif region a and nif region b are needed for full symbiotic effectiveness in R. phaseoli.
authors.affiliation: Departamento de Genética Molecular, Centro de Investigación sobre Fijación de Nitrógeno, Universidad Nacional Autónoma de México, Cuernavaca, Morelos, México, and NifTAL Project, University of Hawaii, Paia, Hawaii 96779.
authors.forename: David
authors.initials: D
authors.lastname: Romero
authors.forename: Paul W
authors.initials: PW
authors.lastname: Singleton
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Segovia
authors.forename: Enrique
authors.initials: E
authors.lastname: Morett
authors.forename: B Ben
authors.initials: BB
authors.lastname: Bohlool
authors.forename: Rafael
authors.initials: R
authors.lastname: Palacios
authors.forename: Guillermo
authors.initials: G
authors.lastname: Dávila