Genetic and environmental control of sexual development in hemiascomycetous yeast Hansenula polymorpha CBS4732.
Kancho Lahchev
Genetics of Microorganisms, Institute of Microbiology, Acad.G.Bontchev 26, Sofia, 1113, Bulgaria
In hemiascomycetous yeast Hansenula polymorpha CBS4732, the transition from vegetative growth to sexual development is a complex process subjected of genetic, physiological, environmental, etc. controls. Compare to the other hemiascomycous yeast, this organism reveal two unusual kinds of homothallism, namely; (i) the ability of any strain to mate with any other strain; and (ii) induction of meiosis and spore formation in monospore (haploid) cultures. The first kind of homothallisms is due to existence of simple tetrapolar mating system, composed from two unlinked mating type loci MATH and MATP. In homozygous state, recessive mating type alleles caused delayed growth of newly formed diploids, differences in colony morphology and inhibition of sporulation rates. Both mating type alleles are stably maintained during mitotic and meiotic divisions and no cases of interconversion among them have been observed. The second kind of homothallism, referred here to as 'haploid sporulation' is a combination of two consecutive but distinct events: self-mating of haploid cells, followed by sporulation of newly formed diploid zygotes. The date presents suggests that H. polymorpha use the switching between vegetative growth and sexual development as specific strategy for survival at harsh environmental conditions.