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Flavonoid-responsive nodY-lacZ expression in three phylogenetically different Bradyrhizobium groups

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Previously, restriction fragment length polymorphism analysis using the nodD1YABC gene probe showed the genetic diversity of common nodD1ABC gene regions of Bradyrhizobium japonicum, Bradyrhizobium elkanii, and the Thai soybean Bradyrhizobium. The nodD1 sequences of representative strains of the 3 groups differed phylogenetically, suggesting that responses of NodD1 proteins of the 3 Bradyrhizobium groups to diverse flavonoids may differ. To confirm this hypothesis, 6 representative strains were chosen from the 3 Bradyrhizobium groups. Six reporter strains were constructed, all carrying the pZB32 plasmid, which contains a nod box and the nodY-lacZ fusion of B. japonicum USDA 110. Differences in nodY-lacZ expression among the strains in response to 37 flavonoid compounds at various concentrations were evaluated. Of those compounds, prunetin (4′,5-dihydroxy-7-methoxyisoflavone) and esculetin (6,7-dihydroxycoumarin) were identified as Bradyrhizobium group-specific nod gene inducers. Esculetin showed nod gene induction activities unique to Thai Bradyrhizobium strains. The levels of nodY-lacZ induction among B. japonicum and Thai Bradyrhizobium strains increased with increasing concentration of prunetin, whereas, those in B. elkanii strains did not.

Précédemment, des analyses en RFLP à l’aide de la sonde nodD1YABC ont démontré l’existence d’une diversité génétique au sein de régions du gène nodD1ABC communes à Bradyrhizobium japonicum, Bradyrhizobium elkanii, et Bradyrhizobium du soya Thaï. Les séquences de nodD1 de souches représentatives des 3 groupes différaient d’un point de vue phylogénique, suggérant que la réponse des protéines NodD1 de ces 3 groupes de Bradyrhizobium à différents flavonoïdes puisse différer. Afin de confirmer cette hypothèse, 6 souches représentatives ont été choisies à partir des 3 groupes de Bradyrhizobium. Six souches rapporteurs comportant toutes le plasmide pZB32 qui contient une boîte nod et un gène de fusion nodY-lacZ de B. japonicum USDA 110 ont été construites. Les différences d’expression de nodY-lacZ en réponse aux 37 composés flavonoïdes utilisés à différentes concentrations ont été évaluées chez ces souches. Parmi ces composés, la prunétine (4′,5-dihydroxy-7-méthoxyisoflavone) et l’esculétine (6,7-dihydroxycoumarin) induisaient le gène nod de façon spécifique aux groupes de Bradyrhizobium. L’esculétine a manifesté une activité d’induction du gène nod spécifique aux souches de Bradyrhizobium Thaï. Les niveaux d’induction de nodY-lacZ chez B. japonicum et chez les souches de Bradyrhizobium Thaï augmentaient en fonction de la concentration de prunétine, contrairement à B. elkanii.

Document Type: Research Article

Publication date: May 1, 2008

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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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