Lim K Yoong, Soltis Douglas E, Soltis Pamela S, Tate Jennifer, Matyasek Roman, Srubarova Hana, Kovarik Ales, Pires J Chris, Xiong Zhiyong, Leitch Andrew R
School of Biological and Chemical Sciences, Queen Mary College, University of London, London, United Kingdom.
PLoS One. 2008;3(10):e3353. doi: 10.1371/journal.pone.0003353. Epub 2008 Oct 9.
Polyploidy, frequently termed "whole genome duplication", is a major force in the evolution of many eukaryotes. Indeed, most angiosperm species have undergone at least one round of polyploidy in their evolutionary history. Despite enormous progress in our understanding of many aspects of polyploidy, we essentially have no information about the role of chromosome divergence in the establishment of young polyploid populations. Here we investigate synthetic lines and natural populations of two recently and recurrently formed allotetraploids Tragopogon mirus and T. miscellus (formed within the past 80 years) to assess the role of aberrant meiosis in generating chromosomal/genomic diversity. That diversity is likely important in the formation, establishment and survival of polyploid populations and species.
METHODOLOGY/PRINCIPAL FINDINGS: Applications of fluorescence in situ hybridisation (FISH) to natural populations of T. mirus and T. miscellus suggest that chromosomal rearrangements and other chromosomal changes are common in both allotetraploids. We detected extensive chromosomal polymorphism between individuals and populations, including (i) plants monosomic and trisomic for particular chromosomes (perhaps indicating compensatory trisomy), (ii) intergenomic translocations and (iii) variable sizes and expression patterns of individual ribosomal DNA (rDNA) loci. We even observed karyotypic variation among sibling plants. Significantly, translocations, chromosome loss, and meiotic irregularities, including quadrivalent formation, were observed in synthetic (S(0) and S(1) generations) polyploid lines. Our results not only provide a mechanism for chromosomal variation in natural populations, but also indicate that chromosomal changes occur rapidly following polyploidisation.
CONCLUSIONS/SIGNIFICANCE: These data shed new light on previous analyses of genome and transcriptome structures in de novo and establishing polyploid species. Crucially our results highlight the necessity of studying karyotypes in young (<150 years old) polyploid species and synthetic polyploids that resemble natural species. The data also provide insight into the mechanisms that perturb inheritance patterns of genetic markers in synthetic polyploids and populations of young natural polyploid species.
多倍体，常被称为“全基因组复制”，是许多真核生物进化中的一股主要力量。事实上，大多数被子植物物种在其进化历史中至少经历过一轮多倍体化。尽管我们在对多倍体诸多方面的理解上取得了巨大进展，但对于染色体分歧在年轻多倍体种群建立中的作用，我们基本上一无所知。在此，我们研究了两个近期反复形成的异源四倍体——米氏婆罗门参（Tragopogon mirus）和杂种婆罗门参（T. miscellus）（在过去80年内形成）的合成系和自然种群，以评估异常减数分裂在产生染色体/基因组多样性中的作用。这种多样性可能在多倍体种群和物种的形成、建立及生存中具有重要意义。
方法/主要发现：荧光原位杂交（FISH）技术在米氏婆罗门参和杂种婆罗门参自然种群中的应用表明，染色体重排和其他染色体变化在这两个异源四倍体中都很常见。我们检测到个体间和种群间广泛的染色体多态性，包括：（i）特定染色体的单体和三体植株（可能表明补偿性三体），（ii）基因组间易位，以及（iii）单个核糖体DNA（rDNA）位点的大小和表达模式的变化。我们甚至在同胞植株间观察到核型变异。值得注意的是，在合成（S(0)和S(1)代）多倍体系中观察到了易位、染色体丢失以及减数分裂异常，包括四价体形成。我们的结果不仅为自然种群中的染色体变异提供了一种机制，还表明染色体变化在多倍体化后迅速发生。
结论/意义：这些数据为之前对新生和正在形成的多倍体物种的基因组和转录组结构分析揭示了新的视角。至关重要的是，我们的结果凸显了研究年轻（<150年）多倍体物种和类似自然物种的合成多倍体核型的必要性。这些数据还为扰乱合成多倍体和年轻自然多倍体物种种群中遗传标记遗传模式的机制提供了见解。
