A MULTIDRUG-RESISTANCE TRANSPORTER SERINE-PROTEASE GENE IS REQUIRED FOR PRESTALK SPECIALIZATION IN DICTYOSTELIUM

The prestalk-specific gene, tagB, was disrupted by restriction enzyme mediated integration (REMI) mutagenesis. Mutant aggregates exhibit a cell-autonomous defect in specialization of PST-A cells, a prestalk subpopulation that forms the tip and eventually forms the stalk of the fruiting body. Cooperative (non-cell-autonomous) defects were found in sporulation and in specialization of prestalk cells that eventually form the upper cup of the fruiting body (PST-O). The pattern of ecmA::lacZ expression in mutant tagB(-) cells defines a primary prestalk population, PST-I, from which other prestalk cells differentiate. After PST-A cells differentiate, they induce remaining PST-I cells to become PST-O cells. Subsequently, prestalk cells induce encapsulation of prespore cells during culmination. tagB is homologous to serine protease and to multidrug resistance (MDR) transporter genes, implying a mechanism of action that includes proteolysis and export of peptide signals. Intercellular communication via TagB may mediate integration of cellular differentiation with morphogenesis.