title: Lotus japonicus cytokinin receptors work partially redundantly to mediate nodule formation.
abstract: Previous analysis of the Lotus histidine kinase1 (Lhk1) cytokinin receptor gene has shown that it is required and also sufficient for nodule formation in Lotus japonicus. The L. japonicus mutant carrying the loss-of-function lhk1-1 allele is hyperinfected by its symbiotic partner, Mesorhizobium loti, in the initial absence of nodule organogenesis. At a later time point following bacterial infection, lhk1-1 develops a limited number of nodules, suggesting the presence of an Lhk1-independent mechanism. We have tested a hypothesis that other cytokinin receptors function in at least a partially redundant manner with LHK1 to mediate nodule organogenesis in L. japonicus. We show here that L. japonicus contains a small family of four cytokinin receptor genes, which all respond to M. loti infection. We show that within the root cortex, LHK1 performs an essential role but also works partially redundantly with LHK1A and LHK3 to mediate cell divisions for nodule primordium formation. The LHK1 receptor is also presumed to partake in mediating a feedback mechanism that negatively regulates bacterial infections at the root epidermis. Interestingly, the Arabidopsis thaliana AHK4 receptor gene can functionally replace Lhk1 in mediating nodule organogenesis, indicating that the ability to perform this developmental process is not determined by unique, legume-specific properties of LHK1.
authors.affiliation: Agriculture and Agri-Food Canada, Southern Crop Protection and Food Research Centre, London, Ontario N5V 4T3, Canada.
authors.forename: Mark
authors.initials: M
authors.lastname: Held
authors.forename: Hongwei
authors.initials: H
authors.lastname: Hou
authors.forename: Mandana
authors.initials: M
authors.lastname: Miri
authors.forename: Christian
authors.initials: C
authors.lastname: Huynh
authors.forename: Loretta
authors.initials: L
authors.lastname: Ross
authors.forename: Md Shakhawat
authors.initials: MS
authors.lastname: Hossain
authors.forename: Shusei
authors.initials: S
authors.lastname: Sato
authors.forename: Satoshi
authors.initials: S
authors.lastname: Tabata
authors.forename: Jillian
authors.initials: J
authors.lastname: Perry
authors.forename: Trevor L
authors.initials: TL
authors.lastname: Wang
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Szczyglowski
mesh_terms: D000483:Alleles; D017360:Arabidopsis / Q000187:drug effects / Q000254:growth & development; D003583:Cytokinins / Q000378:metabolism* / Q000494:pharmacology; D004926:Escherichia coli; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D000070116:Lotus / Q000187:drug effects / Q000235:genetics / Q000254:growth & development* / Q000382:microbiology; D059128:Mesorhizobium; D008954:Models, Biological; D008969:Molecular Sequence Data; D005810:Multigene Family; D009154:Mutation / Q000235:genetics; D038081:Organogenesis / Q000187:drug effects / Q000235:genetics; D010802:Phylogeny; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000235:genetics; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000737:chemistry / Q000378:metabolism*; D053204:Root Nodules, Plant / Q000187:drug effects / Q000254:growth & development* / Q000382:microbiology; D012441:Saccharomyces cerevisiae / Q000235:genetics; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics; D014158:Transcription, Genetic / Q000187:drug effects
chemical_list: D003583:Cytokinins; D010940:Plant Proteins; D012333:RNA, Messenger; D011956:Receptors, Cell Surface