Combining FISH and model-based predictions to understand chromosome evolution in Typhonium (Araceae).
Combining FISH and model-based predictions to understand chromosome evolution in Typhonium (Araceae).
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DOI：
10.1093/aob/mct302
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发表时间：
2014-03
期刊：
影响因子：
4.2
通讯作者：
Aretuza Sousa;N. Cusimano;S. Renner
中科院分区：
文献类型：
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作者：
Aretuza Sousa;N. Cusimano;S. Renner
背景和目的自从分子系统发育学出现以来，人们进行了大量的尝试来推断 DNA 系统发育中染色体数目的进化轨迹。理想情况下，应根据细胞遗传学数据评估此类推论。为了实现这一目标，我们在一个中等规模的天南星科属中进行了染色体数目变化和荧光原位杂交（FISH）的系统发育模型，以阐明来自染色体标记的数据是否支持近亲中染色体数目的最大似然推断变化。 Typhonium 是重点属，包括 2n = 65 和 2n = 8 的物种，这是该科中已知数量最少的物种。方法使用来自核和质体序列（96 个分类单元，4252 个核苷酸）的系统发育和所有包含物种的计数（其中 15 个首次报道）用于模拟染色体数目进化，假设离散事件，例如多倍化和下降或上升的不倍体，以不同的速率发生。使用三种探针（5S rDNA、45S rDNA 和拟南芥样端粒）对 2n = 8 至 2n = 24 的 10 个物种进行 FISH。 主要结果 最佳拟合模型假设过去存在大量染色体数目减少。在用 FISH 分析的物种中，染色体数量最低的两条含有间质端粒信号 (Its)，该信号与系统发育和建模一起表明异倍体减少，作为数量低的解释。模型推断的另一个物种的多倍化与 rDNA 位点的增加相匹配。结论 密集采样的系统发育、祖先状态模型和 FISH 的结合表明，n = 4 的物种是高度衍生的，FISH 数据表明该物种的祖先存在罗伯逊融合样染色体重排。
BACKGROUND AND AIMS Since the advent of molecular phylogenetics, numerous attempts have been made to infer the evolutionary trajectories of chromosome numbers on DNA phylogenies. Ideally, such inferences should be evaluated against cytogenetic data. Towards this goal, we carried out phylogenetic modelling of chromosome number change and fluorescence in situ hybridization (FISH) in a medium sized genus of Araceae to elucidate if data from chromosomal markers would support maximum likelihood-inferred changes in chromosome numbers among close relatives. Typhonium, the focal genus, includes species with 2n = 65 and 2n = 8, the lowest known count in the family. METHODS A phylogeny from nuclear and plastid sequences (96 taxa, 4252 nucleotides) and counts for all included species (15 of them first reported here) were used to model chromosome number evolution, assuming discrete events, such as polyploidization and descending or ascending dysploidy, occurring at different rates. FISH with three probes (5S rDNA, 45S rDNA and Arabidopsis-like telomeres) was performed on ten species with 2n = 8 to 2n = 24. KEY RESULTS The best-fitting models assume numerous past chromosome number reductions. Of the species analysed with FISH, the two with the lowest chromosome numbers contained interstitial telomeric signals (Its), which together with the phylogeny and modelling indicates decreasing dysploidy as an explanation for the low numbers. A model-inferred polyploidization in another species is matched by an increase in rDNA sites. CONCLUSIONS The combination of a densely sampled phylogeny, ancestral state modelling and FISH revealed that the species with n = 4 is highly derived, with the FISH data pointing to a Robertsonian fusion-like chromosome rearrangement in the ancestor of this species.