Expression islands clustered on the symbiosis island of the Mesorhizobium loti genome.
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.
Uchiumi
Toshiki
T
Department of Chemistry and BioScience, Faculty of Science, Kagoshima University, Kagoshima 890-0065, Japan.
Ohwada
Takuji
T
Itakura
Manabu
M
Mitsui
Hisayuki
H
Nukui
Noriyuki
N
Dawadi
Pramod
P
Kaneko
Takakazu
T
Tabata
Satoshi
S
Yokoyama
Tadashi
T
Tejima
Kouhei
K
Saeki
Kazuhiko
K
Omori
Hirofumi
H
Hayashi
Makoto
M
Maekawa
Takaki
T
Sriprang
Rutchadaporn
R
Murooka
Yoshikatsu
Y
Tajima
Shigeyuki
S
Simomura
Kenshiro
K
Nomura
Mika
M
Suzuki
Akihiro
A
Shimoda
Yoshikazu
Y
Sioya
Kouki
K
Abe
Mikiko
M
Minamisawa
Kiwamu
K
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