title: Plant nodulation inducers enhance horizontal gene transfer of Azorhizobium caulinodans symbiosis island.
abstract: 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.
authors.affiliation: Department of Microbiology, College of Life Sciences, Nanjing Agricultural University, Nanjing, Jiangsu 210095, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Ling
authors.affiliation: Department of Microbiology, College of Life Sciences, Nanjing Agricultural University, Nanjing, Jiangsu 210095, China.
authors.forename: Hui
authors.initials: H
authors.lastname: Wang
authors.affiliation: Department of Microbiology, College of Life Sciences, Nanjing Agricultural University, Nanjing, Jiangsu 210095, China.
authors.forename: Ping
authors.initials: P
authors.lastname: Wu
authors.affiliation: Department of Microbiology, College of Life Sciences, Nanjing Agricultural University, Nanjing, Jiangsu 210095, China.
authors.forename: Tao
authors.initials: T
authors.lastname: Li
authors.affiliation: Department of Microbiology, College of Life Sciences, Nanjing Agricultural University, Nanjing, Jiangsu 210095, China.
authors.forename: Yu
authors.initials: Y
authors.lastname: Tang
authors.affiliation: Department of Microbiology, University of Pennsylvania, Philadelphia, PA 19104.
authors.forename: Nawar
authors.initials: N
authors.lastname: Naseer
authors.affiliation: Department of Microbiology, College of Life Sciences, Nanjing Agricultural University, Nanjing, Jiangsu 210095, China.
authors.forename: Huiming
authors.initials: H
authors.lastname: Zheng
authors.affiliation: Institut National de la Recherche Agronomique, UMR 441, Laboratoire des Interactions Plantes-Microorganismes, Castanet-Tolosan 31326, France.
authors.forename: Catherine
authors.initials: C
authors.lastname: Masson-Boivin
authors.affiliation: Department of Microbiology, College of Life Sciences, Nanjing Agricultural University, Nanjing, Jiangsu 210095, China; mol_microb@njau.edu.cn junzhu@upenn.edu.|Institut National de la Recherche Agronomique, UMR 441, Laboratoire des Interactions Plantes-Microorganismes, Castanet-Tolosan 31326, France.
authors.forename: Zengtao
authors.initials: Z
authors.lastname: Zhong
authors.affiliation: Department of Microbiology, College of Life Sciences, Nanjing Agricultural University, Nanjing, Jiangsu 210095, China; mol_microb@njau.edu.cn junzhu@upenn.edu.|Department of Microbiology, University of Pennsylvania, Philadelphia, PA 19104.
authors.forename: Jun
authors.identifier: 0000-0001-9182-5224
authors.initials: J
authors.lastname: Zhu
mesh_terms: D020599:Azorhizobium caulinodans / Q000235:genetics* / Q000378:metabolism; D007887:Fabaceae / Q000235:genetics / Q000382:microbiology; D022761:Gene Transfer, Horizontal / Q000235:genetics*; D044404:Genomic Islands / Q000235:genetics; D009586:Nitrogen Fixation / Q000235:genetics; D055170:Plant Root Nodulation / Q000235:genetics*; D013559:Symbiosis / Q000235:genetics*
keywords: horizontal gene transfer; host-range; integrative and conjugative element; naringenin; nodulation