HOMOTHALLIC LIFE-CYCLE IN THE DIPLOID RED YEAST XANTHOPHYLLOMYCES-DENDRORHOUS (PHAFFIA-RHODOZYMA)

Sexual activity was induced in the basidiomyceteous Phaffia rhodozyma (Xanthophyllomyces dendrorhous) by depletion of nitrogen from the cult ure medium. This activity involved both mating between two yeast cells and the formation of basidiospores. Mating is possibly started by a G 1 phase arrest of the cell cycle, as in other yeasts. The life cycle e xhibited homothallic features. Crosses between genetically marked stra ins, and pulse-field gel electrophoresis of the chromosomal DNA of cel ls derived from individual spores revealed evidence of karyogamy, meio sis and even recombination. The segregation ratio in tetrads pointed t o diploid vegetative cells, which formed tetraploid zygotes and the im mediate meiosis then gave rise to diploid progenies again. Apart from the type strain Phaffia rhodozyma CBS 5905, all the examined strains w ere able to sporulate.