title: Positional cloning identifies Lotus japonicus NSP2, a putative transcription factor of the GRAS family, required for NIN and ENOD40 gene expression in nodule initiation.
abstract: Rhizobia-secreted Nod-factors (NFs) are required for nodulation. In the early developmental process of nodulation, a large number of changes occur in gene expression. Lotus japonicus nsp2 mutants isolated from Gifu B-129 ecotype have defects in nodule initiation and display non-nodulating phenotype. Here, we describe positional cloning of LjNSP2 as a component of the nodulation-specific signaling pathway. LjNSP2 was mapped near the translocation site of chromosome 1 where the recombination is severely suppressed. To circumvent this problem, we introduced Lotus burttii as an alternative crossing partner in place of L. japonicus Miyakojima. The development of the high-resolution map using a total of 11 481 F2 plants, in combination with newly developed DNA markers and construction of BAC library, enabled us to identify the gene responsible for mutant phenotype. LjNSP2 encodes a putative transcription factor of the GRAS family that constitutes a subfamily with Medicago truncatula NSP2. LjNSP2 was expressed in roots and early nodules, but strongly suppressed in matured nodules. The expression analysis of NIN and LjENOD40-1 genes in Ljnsp2 mutants indicates that LjNSP2 functions upstream of these genes. These results suggest that LjNSP2 acts as a transcription factor to directly or indirectly switch on the NF-induced genes required for nodule initiation.
authors.affiliation: National Institute of Agrobiological Sciences, 2-1-2 Kannondai Tsukuba, Ibaraki 305-8602, Japan.
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Murakami
authors.forename: Hiroki
authors.initials: H
authors.lastname: Miwa
authors.forename: Haruko
authors.initials: H
authors.lastname: Imaizumi-Anraku
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kouchi
authors.forename: J Allan
authors.initials: JA
authors.lastname: Downie
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Kawaguchi
authors.forename: Shinji
authors.initials: S
authors.lastname: Kawasaki
mesh_terms: D000595:Amino Acid Sequence; D022202:Chromosomes, Artificial, Bacterial; D003001:Cloning, Molecular; D018506:Gene Expression Regulation, Plant / Q000502:physiology*; D005816:Genetic Complementation Test; D000070116:Lotus / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D053204:Root Nodules, Plant / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors
chemical_list: C403406:NIN protein, Lotus japonicus; D010940:Plant Proteins; D014157:Transcription Factors