Identification of a Diploid Self-sporulating Cycle in the Basidiomycetous Yeast Rhodosporidium toruloides

Abstract

~ Self-sporulating diploid and aneuploid cells were identified in the life cycle of Rhodosporidium toruloides by microscopic observation of nuclear behaviour, microphotometry of DNA content, and genetic characterization of progeny. From a sexual cross between haploid A -and a-type strains, diploid progeny with both A and a mating-type loci and aneuploid progeny with either A or a mating-type locus were isolated in addition to haploid progeny. The diploid isolates propagated by budding in yeast form and eventually developed monokaryotic hyphae. The diploid hyphae formed uninucleate teliospores and blastospores from which diploid yeast cells were isolated (self-sporulatirig). Aneuploids carrying the A or a mating-type isolated from a sexual cross and from self-sporulating diploids entered the sexual cycle like haploid cells. The life cycle consisting of sexual and self-sporulating cycles is presented.Sexual activity was recognized in certain isolates of the yeast Rhodotorula glutinis and these were designated as Rhodosporidium toruloides (Banno, 1967). Our studies of the mating process in this organism (Abe et al., 1975(Abe et al., , 1977 can be summarized as follows. Haploid cells designated as A-and a-type propagate by budding. The cells of A-type constitutively secrete a sexual hormone, rhodotorucine A, which arrests the a-type cells at the G, stage and induces the mating activity. The a-type cells then secrete a sexual hormone, rhodotorucine a. As a result, matingtube formation is induced in both a-and A-type cells in response to mating hormones secreted from cells of opposite mating type, and this is followed by cell-to-cell fusion at the tips of the tubes. After fusion, dikaryotic mycelia and teliospores are developed. Since cellular and nuclear behaviour during the mating process are distinctive, this species is very useful for studying gene expression in relation to cytological changes during sexual differentiation. Isolation of matingless mutants has been reported (Abe et al., 1978), and biochemical analysis in the early stage of sexual differentiation has been attempted (Miyakawa et al., 1982a, b).In the present experiments, self-sporulating progeny were obtained from a sexual cross of haploid A-and a-type strains of R. toruloides. Self-sporulating diploid (SS-type) and aneuploid Aor a-type strains were isolated and classified by genetic and cytological characteristics. METHODS Organisms.Haploid strains of Rhodosporidium toruloides IF0 0559-M-919 (mating-type A, Met-, Pan-, pink colony; designated as M-919) and I F 0 0880-M-1057 (mating-type a, Paba-, yellow colony; M-1057) were used as the parental strains. CCY 62-2-22 (mating-type A , Met-, Phe-, white colony) was also used in one cross. The IF0 and CCY strains were kindly provided by Dr I. Banno (Institute for Fermentation, Osaka, Japan) and by D t A.Kochova-Kratochvilova (Institute for Chemistry, Slovak Academy of Science, Bratislava, Czechoslovakia), respectively.Media and cultivation. The yeast extract/sucrose medium (YS medium) and minimal medium (...

A Deviation from the Bipolar-Tetrapolar Mating Paradigm in an Early Diverged Basidiomycete

“…Self-fertile and asexual strains can be found among natural isolates of red yeasts of the Sporidiobolales [40] , [41] and the origin of the first may be related to the occasional formation of diploid yeast strains. In addition to our present observations, the formation of diploid strains was also previously reported in R. toruloides [51] . However in none of the species studied so far are these diploid states prevailing, leading to the presumption that although these strains do not exhibit obvious growth defects, their genetic makeup may carry some selective disadvantages.…”

Genome sequence of the oleaginous yeast Rhodotorula toruloides strain CGMCC 2.1609

“…These two haploid strains of R. toruloides are very divergent [16] , sharing only 87% identity in genomic nucleotide sequences, despite the fact that they can mate as exemplified by the type strain of R. toruloides [20] . The CGMCC 2.1609 genome sequenced here contains only A1 mating-type information [21] , [22] , which is consistent with aneuploidy observed in progeny from such a mating [23] .…”

Insights into genomics and gene expression of oleaginous yeasts of the genus Rhodoturula

“…In some cases, aneuploid offspring is also a result of chromosomal nondisjunction and non-reciprocal genetic exchanges between the two parental genomes (Dujon, 2010;Gilchrist & Stelkens, 2019). Abe and Sasakuma (1986) identified a diploid self-sporulating cycle in R. toruloides. In that study, cells were observed as diploid or aneuploid in addition to haploid progeny after a sexual cross between the compatible mating types (A1 and A2).…”