Gaudet D A, Gusse J, Laroche A
Research Centre, Agriculture and Agri-Food Canada, P. O. Box 3000, Main, Lethbridge, Alberta, Canada T1J 4B1.
Curr Genet. 1998 Mar;33(3):216-24. doi: 10.1007/s002940050329.
Numerous chromomsome-length polymorphisms (CLPs) associated with chromosome IV were detected in an inbred line of race 8 of Ustilago hordei (teliospore line 1279). Polymorphisms for chromosome IV were observed in the 1600-1900-kb range in approximately 8% of the haploid sporidia originating from this teliospore collection. A monosporidial strain, 1279Ca2, exhibited a new 1620-kb chromosome band and a concurrent loss of the 1950-kb chromosome IV. A ribosomal DNA probe from Armillaria mellea specifically hybridized to both the variant 1620-kb chromosome and to the 1950-kb rDNA chromosome IV in parental strains. Following digestion of chromosome IV with HinfI, the telomere fragments of the 1620-kb chromosome were similar to those of the 1950-kb chromosome IV, indicating that the 1620-kb chromosome arose following a deletion of approximately 330 kb from chromosome IV. The Hinf1 digest of chromosome IV, when probed with the rDNA probe, revealed that much of the rDNA of chromosome IV was lost in the 1279Ca2 line. rDNA sequences were coincidentally recorded in chromosomes I and II in the sister sporidial line, 1279Ca4. When the 1279Ca2 line was mated to other members within the same tetrad and inoculated onto susceptible barley, karyotypes of tetrads and random sporidia originating from the F1 progeny possessed variant chromosomes ranging in size from 1536 to 2110 kb. Among sporidia in 5 of the 12 ordered tetrads sampled, a 1:1 ratio of the 1950-kb parental chromosome IV to the variant chromosome was observed. Within these tetrads, the two polymorphic chromosomes were identical in size and larger than that of the original variant 1620-kb chromosome suggesting that a chromosome expansion, averaging 150 kb, had occurred. In 5 of the 12 tetrads, a 1:1:1:1 ratio representing the two original parents and two recombinant chromosomes was observed, suggesting that normal or unequal recombination had occurred during meiosis. In 2 of the 12 F1 progeny tetrads, the 1950-kb chromosome IVs were apparently eliminated. In karyotypes of these sporidial lines, we observed rDNA sequences in chromosomes I and III that were translocated from chromosome IV. Among 78 random sporidia in the F1 generation, duplication of the variant chromosome IV was observed in three strains. These results suggest that polymorphisms in the rDNA chromosome IV, which consist of chromosome expansion, translocation, and chromosome elimination or duplication, are common in the 1279 strain of U. hordei and its progeny, and that this variability appears to be associated with the tandem-repeat nature of the rDNA sequences.
在大麦坚黑粉菌8号小种的一个自交系（冬孢子系1279）中，检测到了许多与第四条染色体相关的染色体长度多态性（CLP）。在源自该冬孢子群体的大约8%的单倍体担孢子中，观察到第四条染色体在1600 - 1900 kb范围内存在多态性。一个单孢菌株1279Ca2表现出一条新的1620 kb染色体带，同时第四条1950 kb染色体缺失。蜜环菌的核糖体DNA探针与亲本菌株中1620 kb的变异染色体以及1950 kb的第四条rDNA染色体都能特异性杂交。用HinfI酶切第四条染色体后，1620 kb染色体的端粒片段与1950 kb第四条染色体的端粒片段相似，这表明1620 kb染色体是由第四条染色体缺失约330 kb后产生的。用rDNA探针检测第四条染色体的Hinf1酶切产物时发现，在1279Ca2系中，第四条染色体的大部分rDNA丢失了。在姊妹担孢子系1279Ca4的第一条和第二条染色体中，巧合地记录到了rDNA序列。当将1279Ca2系与同一四分体中的其他成员杂交，并接种到感病大麦上时，来自F1后代的四分体和随机担孢子的核型具有大小在1536至2110 kb之间的变异染色体。在抽样的12个有序四分体中的5个的担孢子中，观察到1950 kb的亲本第四条染色体与变异染色体的比例为1:1。在这些四分体内，两条多态性染色体大小相同，且比原来的变异1620 kb染色体大，这表明发生了平均150 kb的染色体扩增。在12个四分体中的5个中，观察到代表两个原始亲本和两条重组染色体的1:1:1:1比例，这表明在减数分裂过程中发生了正常或不等位重组。在12个F1后代四分体中的2个中，1950 kb的第四条染色体显然被消除了。在这些担孢子系的核型中，我们观察到第一条和第三条染色体上的rDNA序列是从第四条染色体易位而来的。在F1代的78个随机担孢子中，在三个菌株中观察到了变异第四条染色体的重复。这些结果表明，第四条rDNA染色体中的多态性，包括染色体扩增、易位以及染色体消除或重复，在大麦坚黑粉菌1279菌株及其后代中很常见，并且这种变异性似乎与rDNA序列的串联重复性质有关。
