期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2016
卷号：113
期号：48
页码：13875-13880
DOI：10.1073/pnas.1615121113
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificancePathogenic or symbiosis islands are mobile genetic elements that can provide recipient bacteria the capacity to establish intimate interactions with eukaryotic hosts. For example, legume symbionts have evolved via horizontal transfer of symbiotic plasmids or genomic islands. Here, we show that the transfer of the symbiosis island of the Sesbania rostrata symbiont, Azorhizobium caulinodans, to other rhizobia is enhanced by plant flavonoids that also serve as signals to initiate the symbiotic process. These data suggest that eukaryotic hosts are involved in bacterial horizontal gene transfer to promote symbiotic interactions between rhizobia and legumes. Horizontal gene transfer (HGT) of genomic islands is a driving force of bacterial evolution. Many pathogens and symbionts use this mechanism to spread mobile genetic elements that carry genes important for interaction with their eukaryotic hosts. However, the role of the host in this process remains unclear. Here, we show that plant compounds inducing the nodulation process in the rhizobium-legume mutualistic symbiosis also enhance the transfer of symbiosis islands. We demonstrate that the symbiosis island of the Sesbania rostrata symbiont, Azorhizobium caulinodans, is an 87.6-kb integrative and conjugative element (ICEAc) that is able to excise, form a circular DNA, and conjugatively transfer to a specific site of gly-tRNA gene of other rhizobial genera, expanding their host range. The HGT frequency was significantly increased in the rhizosphere. An ICEAc-located LysR-family transcriptional regulatory protein AhaR triggered the HGT process in response to plant flavonoids that induce the expression of nodulation genes through another LysR-type protein, NodD. Our study suggests that rhizobia may sense rhizosphere environments and transfer their symbiosis gene contents to other genera of rhizobia, thereby broadening rhizobial host-range specificity.
关键词：horizontal gene transfer ; host-range ; integrative and conjugative element ; naringenin ; nodulation
