Formation of morphological differentiation patterns in the ascomycete Neurospora crassa.

Morphological differentiation patterns--among them concentric rings and radial zonations--can be induced in the band-mutant of Neurospora crassa by appropriate experimental conditions, in particular by a mere shift of certain salt concentrations in the medium. The role of initial experimental conditions is examined and, furthermore, the influences of artificially induced phase differences are analyzed with respect to pattern formation. While the concentric ring pattern is due to some (endogenous) circadian rhythmicity within every hypha, nothing is known about the underlying mechanism of radial zonation development. Various hypotheses were tested with the help of a cellular automaton model which mimics growth, branching and differentiation of a fungal mycelium. In particular, sufficient conditions are provided which imply the formation of radial spore zonations. These conditions postulate a rather homogeneous microscopic hyphal branching pattern and induction of spore differentiation by means of an activator-inhibitor system. Furthermore, a working hypothesis for the formation of spore patterns in Neurospora crassa is suggested which is based on an extracellular control of fungal differentiation.