Chemoattractive Mechanisms in Filamentous Fungi

Research on cell communication and differentiation in filamentous fungi has provided a number of novel insights into chemoattractive mechanisms in recent years. Still, identification of specific chemoattractant molecules, cognate receptors and downstream signaling pathways is strongly biased towards those involved in mating; probably due to the relative ease of functional genomic comparison to the budding yeast model. The multicellular nature of filamentous fungi, however, preserved a more complex morphology compared to unicellular fungi and revealed chemoattractive mechanisms lost during yeast evolution. Two hallmarks of this higher complexity are the formation of an interconnected colony network and the development of elaborate sexual reproductive organs. Morphogenesis of both structures depends on two different modes of chemoattraction: attraction to self and attraction to nonself. Nonself chemoattraction between genetically distinct mating partners is the basis for sexual reproduction and generally regulated through a bilateral sexpheromone/cognate-receptor system, widely but not exclusively equivalent to that known from yeasts. In contrast, selfchemoattraction between genetically identical cells is regulated independently of the sex-pheromone/cognate-receptor systems, and does not exist in yeast. Although both chemoattractive modes do share a number of molecular components, we are only beginning to understand how cell morphogenesis is regulated by means of gene expression and targeted protein recruitment during the establishment of self-fusion. This review provides an overview on the main morphogenetic elements involved in fungal chemoattraction, and summarizes our current understanding of the underlying molecular mechanisms of selfand nonself-fusion during filamentous fungal development.