title: Preferential association of endophytic bradyrhizobia with different rice cultivars and its implications for rice endophyte evolution.
abstract: Plant colonization by bradyrhizobia is found not only in leguminous plants but also in nonleguminous species such as rice. To understand the evolution of the endophytic symbiosis of bradyrhizobia, the effect of the ecosystems of rice plantations on their associations was investigated. Samples were collected from various rice (Oryza sativa) tissues and crop rotational systems. The rice endophytic bradyrhizobia were isolated on the basis of oligotrophic properties, selective medium, and nodulation on siratro (Macroptilium atropurpureum). Six bradyrhizobial strains were obtained exclusively from rice grown in a crop rotational system. The isolates were separated into photosynthetic bradyrhizobia (PB) and nonphotosynthetic bradyrhizobia (non-PB). Thai bradyrhizobial strains promoted rice growth of Thai rice cultivars better than the Japanese bradyrhizobial strains. This implies that the rice cultivars possess characteristics that govern rice-bacterium associations. To examine whether leguminous plants in a rice plantation system support the persistence of rice endophytic bradyrhizobia, isolates were tested for legume nodulation. All PB strains formed symbioses with Aeschynomene indica and Aeschynomene evenia. On the other hand, non-PB strains were able to nodulate Aeschynomene americana, Vigna radiata, and M. atropurpureum but unable to nodulate either A. indica or A. evenia. Interestingly, the nodABC genes of all of these bradyrhizobial strains seem to exhibit low levels of similarity to those of Bradyrhizobium diazoefficiens USDA110 and Bradyrhizobium sp. strain ORS285. From these results, we discuss the evolution of the plant-bradyrhizobium association, including nonlegumes, in terms of photosynthetic lifestyle and nod-independent interactions.
authors.affiliation: School of Biotechnology, Institute of Agricultural Technology, Suranaree University of Technology, Nakhon Ratchasima, Thailand.
authors.forename: Pongdet
authors.initials: P
authors.lastname: Piromyou
authors.affiliation: School of Biotechnology, Institute of Agricultural Technology, Suranaree University of Technology, Nakhon Ratchasima, Thailand.
authors.forename: Teerana
authors.initials: T
authors.lastname: Greetatorn
authors.affiliation: The Center for Scientific and Technological Equipment, Suranaree University of Technology, Nakhon Ratchasima, Thailand.
authors.forename: Kamonluck
authors.initials: K
authors.lastname: Teamtisong
authors.affiliation: Graduate School of Life Sciences, Tohoku University, Sendai, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Okubo
authors.affiliation: Graduate School of Life Sciences, Tohoku University, Sendai, Japan.
authors.forename: Ryo
authors.initials: R
authors.lastname: Shinoda
authors.affiliation: Soil Microbiology Group, Division of Soil Science, Department of Agriculture, Bangkok, Thailand.
authors.forename: Achara
authors.initials: A
authors.lastname: Nuntakij
authors.affiliation: School of Biotechnology, Institute of Agricultural Technology, Suranaree University of Technology, Nakhon Ratchasima, Thailand.
authors.forename: Panlada
authors.initials: P
authors.lastname: Tittabutr
authors.affiliation: School of Biotechnology, Institute of Agricultural Technology, Suranaree University of Technology, Nakhon Ratchasima, Thailand.
authors.forename: Nantakorn
authors.initials: N
authors.lastname: Boonkerd
authors.affiliation: Graduate School of Life Sciences, Tohoku University, Sendai, Japan kiwamu@ige.tohoku.ac.jp neung@sut.ac.th.
authors.forename: Kiwamu
authors.initials: K
authors.lastname: Minamisawa
authors.affiliation: School of Biotechnology, Institute of Agricultural Technology, Suranaree University of Technology, Nakhon Ratchasima, Thailand kiwamu@ige.tohoku.ac.jp neung@sut.ac.th.
authors.forename: Neung
authors.initials: N
authors.lastname: Teaumroong
mesh_terms: D041841:Bradyrhizobiaceae / Q000254:growth & development* / Q000302:isolation & purification* / Q000502:physiology; D060026:Endophytes / Q000254:growth & development* / Q000302:isolation & purification* / Q000502:physiology; D007887:Fabaceae / Q000382:microbiology; D012275:Oryza / Q000382:microbiology*; D063245:Plant Development; D055170:Plant Root Nodulation; D013559:Symbiosis