A NEW MATING COMPATIBILITY LOCUS IN PHYSARUM POLYCEPHALUM

Philip J. Youngman ¹, Dominick J. Pallotta ¹, Betsy Hosler ¹, Gary Struhl ¹, and Charles E. Holt ¹

¹ Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139

The rate and extent of plasmodium formation were studied in mating tests involving pairs of largely isogenic amoebal strains compatible for mating-type (mt) alleles. A systematic variability was observed: plasmodia formed either rapidly and extensively or slowly and inefficiently. Plasmodium formation was found to be 10³- to 10⁴-fold more extensive in "rapid" crosses than in "slow" crosses. A genetic analysis revealed that the variability reflects the influence of a multiallelic compatibility locus that determines mating efficiency. This compatibility locus (designated matB), together with the original mating type locus, mt (in this work designated matA), constitute a tetrapolar mating specificity system in Physarum polycephalum.