title: Nitrogen metabolism in Sinorhizobium meliloti-alfalfa symbiosis: dissecting the role of GlnD and PII proteins.
abstract: To contribute nitrogen for plant growth and establish an effective symbiosis with alfalfa, Sinorhizobium meliloti Rm1021 needs normal operation of the GlnD protein, a bifunctional uridylyltransferase/uridylyl-cleavage enzyme that measures cellular nitrogen status and initiates a nitrogen stress response (NSR). However, the only two known targets of GlnD modification in Rm1021, the PII proteins GlnB and GlnK, are not necessary for effectiveness. We introduced a Tyr→Phe variant of GlnB, which cannot be uridylylated, into a glnBglnK background to approximate the expected state in a glnD-sm2 mutant, and this strain was effective. These results suggested that unmodified PII does not inhibit effectiveness. We also generated a glnBglnK-glnD triple mutant and used this and other mutants to dissect the role of these proteins in regulating the free-living NSR and nitrogen metabolism in symbiosis. The glnD-sm2 mutation was dominant to the glnBglnK mutations in symbiosis but recessive in some free-living phenotypes. The data show that the GlnD protein has a role in free-living growth and in symbiotic nitrogen exchange that does not depend on the PII proteins, suggesting that S. meliloti GlnD can communicate with the cell by alternate mechanisms.
authors.affiliation: Institute of Biological Chemistry, Washington State University, Pullman 99164-6340, USA. syurgel@wsu.edu
authors.forename: Svetlana N
authors.initials: SN
authors.lastname: Yurgel
authors.forename: Jennifer
authors.initials: J
authors.lastname: Rice
authors.forename: Michael L
authors.initials: ML
authors.lastname: Kahn
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D018533:Biomass; D015964:Gene Expression Regulation, Bacterial; D000455:Medicago sativa / Q000382:microbiology* / Q000502:physiology; D009154:Mutation; D009584:Nitrogen / Q000378:metabolism*; D009586:Nitrogen Fixation; D009713:Nucleotidyltransferases / Q000235:genetics / Q000378:metabolism*; D051922:PII Nitrogen Regulatory Proteins / Q000235:genetics / Q000378:metabolism*; D010641:Phenotype; D018517:Plant Roots / Q000382:microbiology / Q000502:physiology; D018520:Plant Shoots / Q000502:physiology; D053204:Root Nodules, Plant / Q000382:microbiology / Q000502:physiology; D016962:Sinorhizobium meliloti / Q000235:genetics / Q000502:physiology*; D013559:Symbiosis
chemical_list: D001426:Bacterial Proteins; D051922:PII Nitrogen Regulatory Proteins; D009713:Nucleotidyltransferases; C022515:regulatory protein uridylyltransferase; D009584:Nitrogen