DIF-1 induces the basal disc of the Dictyostelium fruiting body

The polyketide DIF-1 induces Dictyostelium amoebae to form stalk cells in culture. To better define its role in normal development, we examined the phenotype of a mutant blocking the first step of DIF-1 synthesis, which lacks both DIF-1 and its biosynthetic intermediate, dM-DIF-1 (des-methyl-DIF-1). Slugs of this polyketide synthase mutant (stlB⁻) are long and thin and rapidly break up, leaving an immotile prespore mass. They have ∼ 30% fewer prestalk cells than their wild-type parent and lack a subset of anterior-like cells, which later form the outer basal disc. This structure is missing from the fruiting body, which perhaps in consequence initiates culmination along the substratum. The lower cup is rudimentary at best and the spore mass, lacking support, slips down the stalk. The dmtA⁻ methyltransferase mutant, blocked in the last step of DIF-1 synthesis, resembles the stlB⁻ mutant but has delayed tip formation and fewer prestalk-O cells. This difference may be due to accumulation of dM-DIF-1 in the dmtA⁻ mutant, since dM-DIF-1 inhibits prestalk-O differentiation. Thus, DIF-1 is required for slug migration and specifies the anterior-like cells forming the basal disc and much of the lower cup; significantly the DIF-1 biosynthetic pathway may supply a second signal - dM-DIF-1.