Nuclear Behavior of Rhodosporidium Toruloides, a Heterobasidiomycetous Yeast

Abstract

Nuclear behavior in the cells of Rhodosporidium toruloides, a heterobasidiomycetous yeast, was followed by microscopic observation. The behavior in the process of both asexual and sexual reproduction of the microorganism was found to agree, in principle, with the description on that of Leucosporidium sp., a heterobasidiomycetous yeast. In the artificially induced sexual differentiation in the cells of mating type a strain by A factor (a sex hormone secreted from the cells of mating type A strain), a complete repression of nuclear division occurs with the induction of mating tube formation. As elongation of the tube proceeds, a nucleus moves into the tube from the cell, followed by further migration to the apex of the tube. In the process of artificially induced dedifferentiation by removal of the factor from the incubation medium, the nucleus which was located in the mating tube by previous incubation with the factor recovers the ability to divide into two nuclei without formation of clamp connection. Then the septum formation occurs, followed by emergence of a bud. The bud grows and matures to a yeast cell.In the previous paper (1), we described the cell behavior as a morphological feature during the early stages of mating process of Rhodosporidium toruloides, which belongs to Heterobasidiomycetes and takes the yeast form of cell in the haploid phase, and demonstrated the presence of biologically active compounds, A and a factors, in the culture media of the cells of mating types A and a, respectively. These factors were characterized as sex hormones; A and a factors exclusively induce sexual differentiation in the cells of mating types a and A, respectively. A factor, which is constitutively formed, was partially purified and identified as a peptide (2).In this paper, we describe the cell behavior as the nuclear behavior during the life cycle of this microorganism, and the effect of A factor on cell morphology 175

Differentiation of mating tubes induced by the mating hormone rhodotorucine A during the mitotic cycle of Rhodosporidium toruloides.

“…Mating tube formation from a-mating type cells, which is an early event of the sexual process (2), is induced by a mating hormone, rhodotorucine A (3). Formation and elongation of the mating tubes occur with suppression of bud growth and nuclear duplication, and the cells which form mating tubes are mononucleate (4). Apparently there is a certain critical stage for differentiation of mating tubes in the cell cycle of a-mating type cells before nuclear duplication.…”

“…An agar piece containing the cell-free culture fluid was placed side-by-side between two pieces of M-919 culture (rhodotorucine A-supplying culture containing 2.5 x 10' cells per ml) on a glass slide, and incubated at 27°C for 3 hr. On the other hand, M-1057 cells were adhered to a cover glass as previously described (4), and the side with the adhered M-1057 cells was placed on the piece containing the cell-free culture fluid of M-919, and then cultivated for 5 hr. During the cultivation, the mating hormone was continuously supplied to the target M-1057 cells through agar from M-919 cells which grew in both sides of the agar piece.…”

Sequence of Events in Early Stages of Sexual Differentiation Caused by Rhodotorucine A, a Fungal Sex Hormone: Biological Determi- Nation Using Matingless Mutants Derived From Rhodosporidium Toruloides M 1057

“…When a cells were incubated with rhodotorucine A, the hormone was immediately adsorbed on the cells, followed by the establishment of intracellular information(s) for sexual differentiation within 15 min at 30° (8). After 5-hr incubation with the hormone, occurrence of following four events was clearly detected in a cells : i) Inhibition of bud formation; ii) inhibition of nuclear duplication; iii) formation of mating tube; and (iv) formation of rhodotorucine a in extracellular space (2). In this paper, we describe one trial to determine the sequence of these four events.…”

“…Our previous papers described the biological and chemical aspects on the induction of sexual differentiation in life cycle of heterobasidiomycetous yeasts (1)(2)(3)(4)(5)(6). For example, two kinds of hormones, rhodotorucine A and a, were essentially required for the transference of asexual cycle to sexual cycle in Rhodosporidium toruloides.…”

METHOD FOR ISOLATION OF MATING-LESS MUTANTS FROM RHODOSPORIDIUM TORULOIDES M 1057, A STRAIN OF MATING TYPE a

“…After the cell fusion, secondary hypha formation occurs in the plasmogamete cells, and the hypha grows as dikaryotic cells with clamp connections. In the previous papers, we reported that A and a cells produce extracellular dif fusible substances inducing the formation of mating tubes in the opposite matingtyped cells, a and A cells, respectively (3,4). Recently, rhodotorucine A was isolated from the culture fluid of A cells (5,6), and its chemical structure was confirmed to be (H) Tyr-Pro-Glu-Ile-Ser-Trp-Thr-Arg-Asn-Gly-Cys-S-farnesyl ether (in press in B.B.R.C.).…”