FIGURE 9.

Proposed model of the MtrA regulatory network governing development and differentiation in S. coelicolor. In response to a currently unidentified environmental trigger, MtrA is activated by MtrB phosphorylation, and then the activated MtrA activates chp, rdl, and ram genes and the bldK cluster, the latter of which may also have a positive regulatory effect on the expression of ram, rdl, and chp genes. In contrast, MtrA represses bldD, allowing activation of bldN, a sigma factor gene repressed by BldD-c-di-GMP, and BldN then activates chp and rdl genes, further amplifying the effect of MtrA on the regulation of aerial mycelium formation. MtrA regulates the expression of whiI and whiH, both of which are required for expression of whiE, thus impacting differentiation through the whiIHE pathway. Solid and dotted arrows indicate direct and indirect regulation, respectively. Minus (–) and plus (+) signs indicate a negative or positive role in the regulation of the downstream gene.