XANTHONE INDUCTION OF NOD GENE-EXPRESSION IN BRADYRHIZOBIUM-JAPONICUM

Forty aromatic compounds were tested for their ability to induce nod g ene expression in Bradyrhizobium japonicum. Of these, genistein, bioch anin A, and formononetin have previously been shown to be inducers of both nodD(1)-lacZ and nodY-lacZ expression. In addition, two xanthones -1,3,7-trihydroxyxanthone and 1,6-dihpdroxy-2,8-dimethoxyxanthone, wh ich were isolated from Haploclathra species - were found to be inducer s of nod gene expression. Indeed, 1,6-dihydroxy-2,8-dimethoxyxanthione was as effective as genistein in inducing nodD(1)- and nodY-lacZ expr ession. These xanthone molecules were capable of inducing nod gene exp ression in B. japonicum mutant strain Delta 1267, lacking the nodD(1), nodD(2), and nolA genes. These results suggest that the xanthone indu cers are capable of activating the NodV/W two-component regulatory sys tem known to be essential for nod gene expression in B. japonicum.