MOLECULAR MECHANISM OF PLOIDY-SHIFT AND VARIATION OF COLONY MORPHOLOGY IN THE IMPERFECT YEASTS

某些菌株的白色念珠菌在正常二倍体状态下产生的细胞群中有一定比例具有较高的倍性。该表型被作者命名为Pld^-。在两种不同的倍性状态之间观察到倍性转移。从半扇形菌落弱生长区分离得到Pld- stn21 (arg4, Pld^-)，经STN14紫外线照射后分离得到白色念珠菌CBS5736的arg4衍生物，从另一个正常生长区分离得到STN22 （arg4, Pld^+）。STN22及其祖细胞CBS5736在培养皿中表现出均匀的菌落大小，但STN21在培养早期在YPD板上表现出典型的菌落大小异质性：观察到小菌落和大菌落两种类型。这些菌株的染色体通过PFGE分离出来。部分培养的STN21出现7号染色体单带，可能是由于染色体不分离造成的。另一株培养的STN21出现了一条比7号染色体大的染色体外条带，7号染色体两条条带中有一条缺失。Southern blot杂交实验表明，在染色体外条带上存在位于7号染色体中心的SfiI片段7F，而不存在末端的SfiI片段7C。原生质体融合实验表明，至少存在两个PLD互补基团，其功能可以稳定倍性状态和染色体保真度。

Some strains of Candida albicans poroduce a proportion of the cell population with a higher ploidy than the rest in normal diploid state. This phenotype was named as Pld^-by the author. Ploidy-shift was observed between two different ploidy states. Pld-STN21 (arg4, Pld^-) was isolated from a weakly growing sector of a half-sectored colony, after UV-irradiation of STN14, an arg4 derivative of C.albicans CBS5736 and from the other normally growing sector, STN22 (arg4, Pld^+) was isolated. STN22, as well as its progenitor, CBS5736, showed a homogeneus colony size when plated out, but STN21 showed a characteristic heterogeneity of colony size on YPD plates at an early stage of incubation : two types of colonies, small ones and large ones, were observed.The chromosomes of these strains were separated out by PFGE.Some culture of STN21 showed the single band of chromosome 7, suggesting due to the occurrence of chromosome non-disjunction. The other culture of STN21 gave an extrachromosomal band, the size of which was larger than that of chromosome 7, and the loss of one of the two bands of chromosome 7. Southern blot hybridization experiments showed the existence of a SfiI fragment 7F,a central portion of chromosome 7, on the extrachromosomal band but the absence of a terminal SfiI fragment 7C.Protoplast fusion experiments showed, at least, two complementation groups of PLD,the function of which may stabilize both ploidy state and chromosome fidelity.