Figure 7. Schematic representation summarizing the regulatory network involved in controlling BldM and WhiI expression and the activation of Group-I and Group-II genes.

During vegetative growth, BldD represses bldC, bldN, whiG and bldM. At the onset of differentiation, this repression is relieved, σ^BldN activates bldM and σ^WhiG activates whiI. BldM homodimer activates early sporulation genes such as whiB and ssgR. Subsequently, BldM and WhiI form a heterodimer that activates late sporulation genes such as whiE and smeA-sffA. Thus heterodimer formation serves to integrate signals from two independent pathways (σ^WhiG-WhiI and σ^BldN-BldM). bldM expression is tightly controlled by at least four global regulators - BldD, BldC, σ^BldN and PhoP (a response regulator activated during phosphate depletion [59]).