title: A putative 3-hydroxyisobutyryl-CoA hydrolase is required for efficient symbiotic nitrogen fixation in Sinorhizobium meliloti and Sinorhizobium fredii NGR234.
abstract: We report that the smb20752 gene of the alfalfa symbiont Sinorhizobium meliloti is a novel symbiotic gene required for full N2-fixation. Deletion of smb20752 resulted in lower nitrogenase activity and smaller nodules without impacting overall nodule morphology. Orthologs of smb20752 were present in all alpha and beta rhizobia, including the ngr_b20860 gene of Sinorhizobium fredii NGR234. A ngr_b20860 mutant formed Fix-determinate nodules that developed normally to a late stage of the symbiosis on the host plants Macroptilium atropurpureum and Vigna unguiculata. However an early symbiotic defect was evident during symbiosis with Leucaena leucocephala, producing Fix-indeterminate nodules. The smb20752 and ngr_b20860 genes encode putative 3-hydroxyisobutyryl-CoA (HIB-CoA) hydrolases. HIB-CoA hydrolases are required for l-valine catabolism and appear to prevent the accumulation of toxic metabolic intermediates, particularly methacrylyl-CoA. Evidence presented here and elsewhere (Curson et al., , PLoS ONE 9:e97660) demonstrated that Smb20752 and NGR_b20860 can also prevent metabolic toxicity, are required for l-valine metabolism, and play an undefined role in 3-hydroxybutyrate catabolism. We present evidence that the symbiotic defect of the HIB-CoA hydrolase mutants is independent of the inability to catabolize l-valine and suggest it relates to the toxicity resulting from metabolism of other compounds possibly related to 3-hydroxybutyric acid.
authors.affiliation: Department of Biology, McMaster University, 1280 Main St. W., Hamilton, Ontario, Canada, L8S 4K1.
authors.forename: Maryam
authors.initials: M
authors.lastname: Zamani
authors.affiliation: Department of Biology, McMaster University, 1280 Main St. W., Hamilton, Ontario, Canada, L8S 4K1.
authors.forename: George C
authors.initials: GC
authors.lastname: diCenzo
authors.affiliation: Department of Biology, McMaster University, 1280 Main St. W., Hamilton, Ontario, Canada, L8S 4K1.
authors.forename: Branislava
authors.initials: B
authors.lastname: Milunovic
authors.affiliation: Department of Biology, McMaster University, 1280 Main St. W., Hamilton, Ontario, Canada, L8S 4K1.
authors.forename: Turlough M
authors.initials: TM
authors.lastname: Finan
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D000455:Medicago sativa / Q000382:microbiology; D009586:Nitrogen Fixation; D042181:Sinorhizobium fredii / Q000201:enzymology / Q000235:genetics / Q000502:physiology*; D016962:Sinorhizobium meliloti / Q000201:enzymology / Q000235:genetics / Q000502:physiology*; D013559:Symbiosis; D013869:Thiolester Hydrolases / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D013869:Thiolester Hydrolases; C035908:3-hydroxyisobutyryl-CoA hydrolase