title: Characterization of four lectin-like receptor kinases expressed in roots of Medicago truncatula. Structure, location, regulation of expression, and potential role in the symbiosis with Sinorhizobium meliloti.
abstract: To study the role of LecRK (lectin-like receptor kinase) genes in the legumerhizobia symbiosis, we have characterized the four Medicago truncatula Gaernt. LecRK genes that are most highly expressed in roots. Three of these genes, MtLecRK7;1, MtLecRK7;2, and MtLecRK7;3, encode proteins most closely related to the Class A LecRKs of Arabidopsis, whereas the protein encoded by the fourth gene, MtLecRK1;1, is most similar to a Class B Arabidopsis LecRK. All four genes show a strongly enhanced root expression, and detailed studies on MtLecRK1;1 and MtLecRK7;2 revealed that the levels of their mRNAs are increased by nitrogen starvation and transiently repressed after either rhizobial inoculation or addition of lipochitooligosaccharidic Nod factors. Studies of the MtLecRK1;1 and MtLecRK7;2 proteins, using green fluorescent protein fusions in transgenic M. truncatula roots, revealed that they are located in the plasma membrane and that their central transmembrane-spanning helix is required for correct sorting. Moreover, their lectin-like domains appear to be highly glycosylated. Of the four proteins, only MtLecRK1;1 shows a high conservation of key residues implicated in monosaccharide binding, and molecular modeling revealed that this protein may be capable of interacting with Nod factors. However, no increase in Nod factor binding was found in roots overexpressing a fusion in which the kinase domain of this protein had been replaced with green fluorescent protein. Roots expressing this fusion protein however showed an increase in nodule number, suggesting that expression of MtLecRK1;1 influences nodulation. The potential role of LecRKs in the legume-rhizobia symbiosis is discussed.
authors: Laboratoire des Interactions Plantes-Microorganismes, Institut National de la Recherche Agronomique-Centre National de la Recherche Scientifique, Boite Postale 27, 31326 Castanet-Tolosan cedex, France.
authors: Maria-Teresa
authors: MT
authors: Navarro-Gochicoa
authors: Sylvie
authors: S
authors: Camut
authors: Antonius C J
authors: AC
authors: Timmers
authors: Andreas
authors: A
authors: Niebel
authors: Christine
authors: C
authors: Herve
authors: Emmanuel
authors: E
authors: Boutet
authors: Jean-Jacques
authors: JJ
authors: Bono
authors: Anne
authors: A
authors: Imberty
authors: Julie V
authors: JV
authors: Cullimore
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D017124:Conserved Sequence; D015971:Gene Expression Regulation, Enzymologic / Q000235:genetics; D018506:Gene Expression Regulation, Plant / Q000235:genetics*; D029902:Medicago / Q000145:classification / Q000201:enzymology* / Q000235:genetics / Q000502:physiology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010802:Phylogeny; D037121:Plant Lectins / Q000737:chemistry / Q000235:genetics*; D018517:Plant Roots / Q000201:enzymology*; D011487:Protein Conformation; D011494:Protein Kinases / Q000737:chemistry / Q000235:genetics*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D016962:Sinorhizobium meliloti / Q000502:physiology*; D013559:Symbiosis
chemical_list: D037121:Plant Lectins; D011494:Protein Kinases