Comparative Genome-Wide Transcriptional Profiling of Azorhizobium caulinodans ORS571 Grown under Free-Living and Symbiotic Conditions
Comparative Genome-Wide Transcriptional Profiling of Azorhizobium caulinodans ORS571 Grown under Free-Living and Symbiotic Conditions
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DOI：
10.1128/aem.00398-09
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发表时间：
2009-06
影响因子：
4.4
通讯作者：
S. Tsukada;T. Aono;N. Akiba;Kyung-Bum Lee;Chi-Te Liu;Hiroki Toyazaki;H. Oyaizu
中科院分区：
文献类型：
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作者：
S. Tsukada;T. Aono;N. Akiba;Kyung-Bum Lee;Chi-Te Liu;Hiroki Toyazaki;H. Oyaizu
摘要最近测定了在田菁茎和根上形成固氮根瘤的内共生细菌固氮根瘤菌ORS571的全基因组序列。基因组和共生岛的大小分别为5.4Mb和86.7kb，是所测得的根瘤菌中最小的。在本研究中，构建了茎瘤拟杆菌的全基因组芯片，并对生长在丰富和微量培养基中的自由细胞和从茎瘤中分离的类杆菌进行了转录转录分析。转录图谱显示，与硫吸收和代谢、丙酮代谢和胞外多糖生物合成相关的基因在类杆菌中的表达水平高于在自由细胞中的表达水平。在我们之前的研究中，我们获得了一些在这些基因中含有TN5转座子的突变体，它们的表达增加了，成为了根瘤缺陷突变体。此外，还对生长在添加了柚皮苷元的最低限度培养基中的自由生活细胞进行了转录转录分析，柚皮苷元是茎瘤拟青霉nod基因最有效的诱导剂之一。仅有18个基因在加入柚皮苷元后表达增加，这表明对黄酮类化合物作出响应的调控机制在茎突圆线虫中可能很简单。我们的全基因组转录图谱和我们以前的全基因组突变研究相结合，揭示了结核形成和维持的新方面。
ABSTRACT The whole-genome sequence of the endosymbiotic bacterium Azorhizobium caulinodans ORS571, which forms nitrogen-fixing nodules on the stems and roots of Sesbania rostrata, was recently determined. The sizes of the genome and symbiosis island are 5.4 Mb and 86.7 kb, respectively, and these sizes are the smallest among the sequenced rhizobia. In the present study, a whole-genome microarray of A. caulinodans was constructed, and transcriptomic analyses were performed on free-living cells grown in rich and minimal media and in bacteroids isolated from stem nodules. Transcriptional profiling showed that the genes involved in sulfur uptake and metabolism, acetone metabolism, and the biosynthesis of exopolysaccharide were highly expressed in bacteroids compared to the expression levels in free-living cells. Some mutants having Tn5 transposons within these genes with increased expression were obtained as nodule-deficient mutants in our previous study. A transcriptomic analysis was also performed on free-living cells grown in minimal medium supplemented with a flavonoid, naringenin, which is one of the most efficient inducers of A. caulinodans nod genes. Only 18 genes exhibited increased expression by the addition of naringenin, suggesting that the regulatory mechanism responding to the flavonoid could be simple in A. caulinodans. The combination of our genome-wide transcriptional profiling and our previous genome-wide mutagenesis study has revealed new aspects of nodule formation and maintenance.