UNCONTROLLED GROWTH-ASSOCIATED WITH NOVEL SOMATIC RECOMBINATION IN THE FUNGUS SCHIZOPHYLLUM

In the bracket mushroom, Schizophyllum commune, a recessive genetic al teration, mnd, causes abnormally hyperplastic three-dimensional mounds of hyphae to rise from the surface of both haploid and dikaryotic myc elia. mnd, although not a genetic block in the fruiting body developme ntal pathway, is at least partially epistatic to fruiting. Within dika ryons containing both mutant and wild-type nuclei, [mnd + mnd(+)], a n onreciprocal somatic recombination event can lead to stable conversion of the mnd(+) region of the wild-type nucleus to mild. This transform ation to the homoallelic [mnd + mnd] condition involves no genomic are as other than the mild region and permanently prevents any further fru iting. Studies relating to the recombination mechanism have ruled out a diploid intermediate state and other concomitants of orthodox somati c recombination, as well as whole chromosome transfer. Instead, a nove l form of internuclear genetic transfer is postulated whereby a nearby locus, mob(+), controls the mobilization of the mnd chromosomal regio n alone from one nucleus to the other within the binucleate cells of d ikaryotic mycelia.