Expression Islands Clustered on the Symbiosis Island of the Mesorhizobium loti Genome
Expression Islands Clustered on the Symbiosis Island of the Mesorhizobium loti Genome
复制标题
DOI：
10.1128/jb.186.8.2439-2448.2004
复制
发表时间：
2004-04
影响因子：
3.2
通讯作者：
T. Uchiumi;T. Ohwada;Manabu Itakura;H. Mitsui;Noriyuki Nukui;Pramod Dawadi;T. Kaneko;S. Tabata;T. Yokoyama;Kouhei Tejima;K. Saeki;H. Omori;M. Hayashi;T. Maekawa;Rutchadaporn Sriprang;Y. Murooka;S. Tajima;Kenshiro Simomura;M. Nomura;A. Suzuki;Y. Shimoda;Kouki Sioya;M. Abe;K. Minamisawa
中科院分区：
文献类型：
--
作者：
T. Uchiumi;T. Ohwada;Manabu Itakura;H. Mitsui;Noriyuki Nukui;Pramod Dawadi;T. Kaneko;S. Tabata;T. Yokoyama;Kouhei Tejima;K. Saeki;H. Omori;M. Hayashi;T. Maekawa;Rutchadaporn Sriprang;Y. Murooka;S. Tajima;Kenshiro Simomura;M. Nomura;A. Suzuki;Y. Shimoda;Kouki Sioya;M. Abe;K. Minamisawa
根瘤菌是与寄主豆科植物相关的共生固氮土壤细菌。根瘤菌共生的建立需要在微氧环境中伙伴之间的信号交换，从而使两个伙伴互惠共生。我们开发了一种名为loti Mesorhizobium MAFF303099的宏阵列（macroarray），并监测了该细菌在共生、微生物共生和饥饿期间的转录动态。全球转录谱分析表明，共生岛（611 kb）内的基因簇在共生过程中集体表达，而岛外的基因则下调。共生岛是一个与其他染色体区域不同的可传递区域。这一发现表明，巨大的共生岛作为集群表达岛的功能支持共生固氮。有趣的是，共生岛上的大多数转座酶基因在类杆菌中高度上调，如nif、fix、fdx和rpoN。共生岛外包含fixNOPQ基因的基因组区域作为另一个表达岛在微氧和共生条件下均显著上调。共生分析数据表明，氨基酸代谢被激活，以及nif-fix基因的表达。相比之下，细胞壁合成、细胞分裂、DNA复制和鞭毛基因在分化的类细菌中被强烈抑制。在类细菌中，编码1-氨基环丙烷-1-羧酸脱氨酶的基因mlr5932被破坏，并被证实与结瘤增强有关，这表明破坏高表达基因是探索共生中新基因功能的有用策略。
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.