Genistein-Dependent Regulatory Circuits in Bradyrhizobium japonicum
The B. japonicum genome consists of a single circular chromosome (Kaneko et al., 2002). The regulation of genes directly involved in nodulation (nod) is well studied (Figure 1; Loh and Stacey, 2003). Genistein is a potent signal molecule of soybean. In B. japonicum, two regulatory systems are required for efficient symbiosis. NodD1, a LysR-type regulator, is a well-conserved activator protein in rhizobia. NodVW, belonging to the two-component regulatory family, are essential for the nodulation of several host plants (Göttfert et al., 1990). nwsB, if overexpressed, could repress the Nod− phenotype of the nodW (Grob et al., 1993). nwsB is also involved in nodulation-density-dependent repression of nod genes (Loh et al., 2002). NolA and NodD2 mediate this effect (Loh et al., 2001).