Martin Francis, Selosse Marc-André, Tacon Francois Le
Microbiology (Reading). 1999 Jul;145 ( Pt 7):1605-1611. doi: 10.1099/13500872-145-7-1605.
The nuclear rDNA intergenic spacer (IGS) of the ectomycorrhizal basidiomycete Laccaria bicolor was amplified and sequenced to identify the source of its intraspecific polymorphism. The IGS was amplified by PCR in several L. bicolor strains and shown to exhibit multiple bands and length polymorphism. The IGS loci were shown to segregate in a 1:1 ratio within haploid progenies in three dikaryotic strains, suggesting that divergent IGS haplotypes were present in the two nuclei of these strains. The two haplotypes of L. bicolor S238N were sequenced: the beta-haplotype was 4160 bp in length, whereas the size of the alpha-haplotype was estimated to be about 4700 bp. These represent the largest published fungal IGS sequences to date. These sequences can be subdivided into three main regions, IGS1, 5S rDNA and IGS2. The IGS sequences are AT-rich and contain numerous occurrences of three types of subrepeats (e.g. T2-AC3). The length polymorphism, observed between the IGS sequence of the alpha- and beta-haplotypes, results from the insertion of various numbers of a 71 bp subrepeat, called B, occurring in IGS2. This variation in subrepeat number suggests that the two haplotypes resulted from unequal cross-overs. The L. bicolor IGS was aligned with IGS sequences of two other Tricholomataceae (i.e. Tricholoma matsutake and Collybia fusipes). No sequence similarity was observed between these IGSs, but homologous subrepeats were found in L. bicolor and T. matsutake. Analysis of IGS length polymorphism is therefore an efficient tool for investigating genetic relationships between genets and within progenies in natural fungal populations.
为了确定外生菌根担子菌双色蜡蘑种内多态性的来源，对其核糖体DNA基因间隔区（IGS）进行了扩增和测序。通过PCR在多个双色蜡蘑菌株中扩增了IGS，结果显示其呈现多条带和长度多态性。在三个双核菌株的单倍体子代中，IGS位点以1:1的比例分离，这表明这些菌株的两个细胞核中存在不同的IGS单倍型。对双色蜡蘑S238N的两种单倍型进行了测序：β-单倍型长度为4160 bp，而α-单倍型的大小估计约为4700 bp。这些是迄今为止已发表的最大的真菌IGS序列。这些序列可细分为三个主要区域，即IGS1、5S rDNA和IGS2。IGS序列富含AT，并且包含三种类型的亚重复序列（例如T2-AC3）的大量出现。α-和β-单倍型的IGS序列之间观察到的长度多态性，是由于IGS2中插入了不同数量的71 bp亚重复序列（称为B）所致。亚重复序列数量的这种变化表明，这两种单倍型是由不等交换产生的。将双色蜡蘑的IGS与另外两种口蘑科真菌（即松口蘑和梭柄乳头蘑）的IGS序列进行了比对。这些IGS之间未观察到序列相似性，但在双色蜡蘑和松口蘑中发现了同源亚重复序列。因此，分析IGS长度多态性是研究天然真菌种群中不同遗传个体之间以及子代内部遗传关系的有效工具。
