The postulated phosphorelay that regulates the spore germination program. DHKC and DHKB are sensory histidine kinases; RDEA is a histidine-containing phospho-transfer protein; REGA is the response regulator possessing activatable cAMP-phosphodiesterase activity; and PKA is cAMP-dependent protein kinase A. Although the presence of ammonia activates DHKC to transfer phosphates to REGA, discadenine stimulates a phosphatase activity of DHKB which drains the phosphorelay. This is shown here to occur at RDEA, however the phosphatase activity may work on DHKC-P or REGA-P. Discadenine is an autoinhibitor of germination that is produced by maturing spore cells and that accumulates within the sorus. Once discadenine is removed after dispersal of spores, the autokinase activities of both DHKB and DHKC result in the transfer of phosphates to REGA which in turn results in the lowering of the cAMP concentration, the inactivation of PKA, and spore germination may now occur. ACA and ACG are adenylyl cyclases, the latter of which is activated by high osmolarity within the sorus.

A more general model of how the DHKB and DHKC phosphorelays are involved in controling various developmental phenomena can be found elsewhere.