FIG 7.

A working model showing how CBC and CrzA reversely regulate vegetative growth and asexual reproduction in liquid-submerged culture. When the transcription factor CBC is present (top), it represses the brlA-associated central regulatory pathway in combination with its upstream regulators fluG, flbD, and flbC, and crzA (encoding the calcium-responsive transcription factor CrzA). Meanwhile, the cytosolic Ca²⁺ concentration is at a low level (Ca²⁺ homeostasis), which represses the dephosphorylation of CrzA and its translocation to the nucleus. In this situation, A. fumigatus undergoes constant vegetative growth in liquid-submerged culture. When CBC is absent, the expressive suppression of the upstream and central regulator in the conidiation pathways and crzA is stopped. Additionally, the absence of CBC also causes enhanced transient cytosolic Ca²⁺ levels and activates conidiation-positive inducer Ca²⁺-CrzA modules to further elevate the expression of the indicated genes. As a result, asexual conidiation is activated.