title: Identification and functional analysis of type III effector proteins in Mesorhizobium loti.
abstract: Mesorhizobium loti MAFF303099, a microsymbiont of the model legume Lotus japonicus, possesses a cluster of genes (tts) that encode a type III secretion system (T3SS). In the presence of heterologous nodD from Rhizobium leguminosarum and a flavonoid naringenin, we observed elevated expression of the tts genes and secretion of several proteins into the culture medium. Inoculation experiments with wild-type and T3SS mutant strains revealed that the presence of the T3SS affected nodulation at a species level within the Lotus genus either positively (L. corniculatus subsp. frondosus and L. filicaulis) or negatively (L. halophilus and two other species). By inoculating L. halophilus with mutants of various type III effector candidate genes, we identified open reading frame mlr6361 as a major determinant of the nodulation restriction observed for L. halophilus. The predicted gene product of mlr6361 is a protein of 3,056 amino acids containing 15 repetitions of a sequence motif of 40 to 45 residues and a shikimate kinase-like domain at its carboxyl terminus. Homologues with similar repeat sequences are present in the hypersensitive-response and pathogenicity regions of several plant pathogens, including strains of Pseudomonas syringae, Ralstonia solanacearum, and Xanthomonas species. These results suggest that L. halophilus recognizes Mlr6361 as potentially pathogen derived and subsequently halts the infection process.
authors.affiliation: Department of Biological Sciences, Faculty of Science, Nara Women's University, Nara 630-8506, Japan.
authors.forename: Shin
authors.initials: S
authors.lastname: Okazaki
authors.forename: Saori
authors.initials: S
authors.lastname: Okabe
authors.forename: Miku
authors.initials: M
authors.lastname: Higashi
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Shimoda
authors.forename: Shusei
authors.initials: S
authors.lastname: Sato
authors.forename: Satoshi
authors.initials: S
authors.lastname: Tabata
authors.forename: Masatsugu
authors.initials: M
authors.lastname: Hashiguchi
authors.forename: Ryo
authors.initials: R
authors.lastname: Akashi
authors.forename: Michael
authors.initials: M
authors.lastname: Göttfert
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Saeki
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D000070116:Lotus / Q000382:microbiology; D005810:Multigene Family / Q000502:physiology*; D016366:Open Reading Frames / Q000502:physiology*; D017434:Protein Structure, Tertiary / Q000502:physiology; D012230:Rhizobiaceae / Q000235:genetics / Q000378:metabolism*; D055571:Secretory Pathway / Q000502:physiology*; D017386:Sequence Homology, Amino Acid; D013559:Symbiosis / Q000502:physiology
chemical_list: D001426:Bacterial Proteins