Genetic regulation of differentiation inPhysarum polycephalum

Abstract

SUMMARYPlasmodial formation in the MyxomycetePhysarum polycephalumis controlled by a mating type (mt) locus. There are a number of different heterothallicmtalleles; and also a variant,mth, that allows plasmodial formation in pure clones. This paper reports an analysis of this differentiation system. The strainCL(mth) forms plasmodia in pure clones (i.e. it selfs).CLwas mutagenized with NMG and 21 mutants unable to differentiate into amoebae were isolated. The mutants, together withCLd, fell into two complementation groups, twelve indifAand ten indifB. Both complementation groups are closely linked or allelic to themtlocus.difArepresents a gene essential for plasmoclial formation, but it is suggested thatdifBrepresents a class of revertants to themt2heterothallic state. A model of the control of plasmodial formation is proposed in which themtlocus is suggested to code for the repressor of thedifAgene. Genetic control is explained in terms of the dilution of allele-specific repressors.