Autocrine pheromone signalling regulates community behaviour in the fungal pathogen Fusarium oxysporum.

Autocrine self-signalling via secreted peptides and cognate receptors regulates cell development in eukaryotes and is conserved from protozoans to mammals. In contrast, secreted peptides from higher fungi have been traditionally associated with paracrine non-self-signalling during sexual reproduction. For example, cells of the model fungus Saccharomyces cerevisiae fall into two distinct mating types (MAT), which produce either a- or α-pheromone and the cognate receptors Ste2 or Ste3, respectively. Inappropriate autocrine pheromone signalling (APS) during mating is prevented by downregulation of the self-pheromone receptor and by a-type cell-specific cleavage of α-pheromone through the protease Bar1 (refs. ). While APS can be artificially induced by manipulation of the pheromone secrete-and-sense circuit, its natural occurrence in ascomycete fungi has not been described. Here, we show that Fusarium oxysporum-a devastating plant pathogen that lacks a known sexual cycle-co-expresses both pheromone-receptor pairs, resulting in autocrine regulation of developmental programmes other than mating. We found that unisexual populations of MAT1-1 cells (α-type idiomorphs) secrete and sense both a- and α-pheromone, and that their perception requires the cognate receptors and conserved elements of the cell wall integrity mitogen-activated protein kinase cascade. We further show that F. oxysporum uses APS to regulate spore germination in a cell-density-dependent manner, whereby the α-Ste2 interaction leads to repression of conidial germination while the a-Ste3 interaction relieves repression. Our results reveal the existence of a regulatory function for peptide pheromones in the quorum-sensing-mediated control of fungal development.