title: Expression islands clustered on the symbiosis island of the Mesorhizobium loti genome.
abstract: Rhizobia are symbiotic nitrogen-fixing soil bacteria that are associated with host legumes. The establishment of rhizobial symbiosis requires signal exchanges between partners in microaerobic environments that result in mutualism for the two partners. We developed a macroarray for Mesorhizobium loti MAFF303099, a microsymbiont of the model legume Lotus japonicus, and monitored the transcriptional dynamics of the bacterium during symbiosis, microaerobiosis, and starvation. Global transcriptional profiling demonstrated that the clusters of genes within the symbiosis island (611 kb), a transmissible region distinct from other chromosomal regions, are collectively expressed during symbiosis, whereas genes outside the island are downregulated. This finding implies that the huge symbiosis island functions as clustered expression islands to support symbiotic nitrogen fixation. Interestingly, most transposase genes on the symbiosis island were highly upregulated in bacteroids, as were nif, fix, fdx, and rpoN. The genome region containing the fixNOPQ genes outside the symbiosis island was markedly upregulated as another expression island under both microaerobic and symbiotic conditions. The symbiosis profiling data suggested that there was activation of amino acid metabolism, as well as nif-fix gene expression. In contrast, genes for cell wall synthesis, cell division, DNA replication, and flagella were strongly repressed in differentiated bacteroids. A highly upregulated gene in bacteroids, mlr5932 (encoding 1-aminocyclopropane-1-carboxylate deaminase), was disrupted and was confirmed to be involved in nodulation enhancement, indicating that disruption of highly expressed genes is a useful strategy for exploring novel gene functions in symbiosis.
authors.affiliation: Department of Chemistry and BioScience, Faculty of Science, Kagoshima University, Kagoshima 890-0065, Japan.
authors.forename: Toshiki
authors.initials: T
authors.lastname: Uchiumi
authors.forename: Takuji
authors.initials: T
authors.lastname: Ohwada
authors.forename: Manabu
authors.initials: M
authors.lastname: Itakura
authors.forename: Hisayuki
authors.initials: H
authors.lastname: Mitsui
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Nukui
authors.forename: Pramod
authors.initials: P
authors.lastname: Dawadi
authors.forename: Takakazu
authors.initials: T
authors.lastname: Kaneko
authors.forename: Satoshi
authors.initials: S
authors.lastname: Tabata
authors.forename: Tadashi
authors.initials: T
authors.lastname: Yokoyama
authors.forename: Kouhei
authors.initials: K
authors.lastname: Tejima
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Saeki
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Omori
authors.forename: Makoto
authors.initials: M
authors.lastname: Hayashi
authors.forename: Takaki
authors.initials: T
authors.lastname: Maekawa
authors.forename: Rutchadaporn
authors.initials: R
authors.lastname: Sriprang
authors.forename: Yoshikatsu
authors.initials: Y
authors.lastname: Murooka
authors.forename: Shigeyuki
authors.initials: S
authors.lastname: Tajima
authors.forename: Kenshiro
authors.initials: K
authors.lastname: Simomura
authors.forename: Mika
authors.initials: M
authors.lastname: Nomura
authors.forename: Akihiro
authors.initials: A
authors.lastname: Suzuki
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Shimoda
authors.forename: Kouki
authors.initials: K
authors.lastname: Sioya
authors.forename: Mikiko
authors.initials: M
authors.lastname: Abe
authors.forename: Kiwamu
authors.initials: K
authors.lastname: Minamisawa
mesh_terms: D000332:Aerobiosis; D001483:Base Sequence; D020869:Gene Expression Profiling; D016680:Genome, Bacterial; D000070116:Lotus / Q000382:microbiology*; D008969:Molecular Sequence Data; D005810:Multigene Family; D009586:Nitrogen Fixation / Q000235:genetics*; D020411:Oligonucleotide Array Sequence Analysis; D010641:Phenotype; D012230:Rhizobiaceae / Q000235:genetics*; D013559:Symbiosis / Q000235:genetics*; D014158:Transcription, Genetic