Microbes and Environments
Online ISSN : 1347-4405
Print ISSN : 1342-6311
ISSN-L : 1342-6311
Regular Papers
Involvement of a Novel Genistein-Inducible Multidrug Efflux Pump of Bradyrhizobium japonicum Early in the Interaction with Glycine max (L.) Merr
Keisuke TakeshimaTatsuo HidakaMin WeiTadashi YokoyamaKiwamu MinamisawaHisayuki MitsuiManabu ItakuraTakakazu KanekoSatoshi TabataKazuhiko SaekiHirofumi OomoriShigeyuki TajimaToshiki UchiumiMikiko AbeYoshihiko TokujiTakuji Ohwada
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2013 Volume 28 Issue 4 Pages 414-421


The early molecular dialogue between soybean and the bacterium Bradyrhizobium japonicum is crucial for triggering their symbiotic interaction. Here we found a single large genomic locus that is widely separated from the symbiosis island and was conspicuously induced within minutes after the addition of genistein. This locus (named BjG30) contains genes for the multidrug efflux pump, TetR family transcriptional regulator, and polyhydroxybutyrate (PHB) metabolism. The induction of BjG30 by genistein was competitively inhibited by daidzein, although both genistein and daidzein are soybean-derived inducers of nodulation (nod) genes. Such a differential expression pattern is also observed in some legume-derived flavonoids, which structurally differ in the hydroxy/deoxy group at the 5-position. In addition, not only did the induction start far in advance of nodW and nodD1 after the addition of genistein, but the levels showed distinct concentration dependence, indicating that the induction pattern of BjG30 is completely different from that of nod genes. The deletion of genes encoding either the multidrug efflux pump or PHB metabolism, especially the former, resulted in defective nodulation performance and nitrogen-fixing capability. Taken together, these results indicate that BjG30, and especially its multidrug efflux pump, may play a key role in the early stage of symbiosis by balancing the dual functions of genistein as both a nod gene inducer and toxicant.

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© 2013 Japanese Society of Microbial Ecology / Japanese Society of Soil Microbiology / Taiwan Society of Microbial Ecology
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