Signal transduction cascades regulating fungal development and virulence

Cellular differentiation, mating and filamentous growth are regulated in ma ny fungi by environmental and nutritional signals. For example, in response to nitrogen limitation, diploid cells of the yeast Saccharomyces cerevisia e undergo a dimorphic transition to filamentous growth referred to as pseud ohyphal differentiation. Yeast filamentous growth is regulated, in part by two conserved signal transduction cascades: a mitogen-activated protein kin ase cascade and a G-protein regulated cyclic AMP signaling pathway. Related signaling cascades play an analogous role in regulating mating and virulen ce in the plant fungal pathogen Ustilago maydis and the human fungal pathog ens Cryptococcus neoformans and Candida albicans. We review here studies on the signaling cascades that regulate development of these and other fungi. This analysis illustrates both how the model yeast S, cerevisiae can serve as a paradigm for signaling in other organisms and also how studies in oth er fungi provide insights into conserved signaling pathways that operate in many divergent organisms.