Extremes in chromosome numbers in closely related taxa: A combined approach to studying the underlying karyotype evolution

关于植物基因组的一个长期存在的问题是，一些群体如何在数量巨大的染色体上组织他们的基因内容，有时在很短的进化时间跨度内。这是我们提出的问题，在这里，使用天南星属独角莲作为一个研究系统。亚洲的犁头尖有2n = 10，澳大利亚的犁头尖有2n = 160，这些是该科中最低和几乎最高的数字。新的和公布的计数也意味着一个广泛的基础染色体数目在犁头尖属。在犁头尖属的多位点染色体发生中，2n = 10的物种嵌入具有较高染色体数目的物种中，这意味着染色体丢失或融合，而高计数意味着多轮多倍化。我们建议调查（i）核型重排，导致染色体数目减少或倍增;（ii）伴随染色体数目变化的基因组大小变化;和（iii）基因组大小和/或染色体数目变化的进化背景（例如，时间和地点，根据染色体发生学估计）。将使用的技术是分子遗传学、基因组大小测量和重复DNA序列的荧光原位杂交（FISH）。试点FISH数据，使用我们的大量收集的材料栽培的犁头尖，证明适合犁头尖作为一个系统的基因组进化。

A long-standing question about plant genomes is how some groups have managed to organize their gene content on tremendously varying numbers of chromosomes, sometimes over short evolutionary time spans. This is the question we propose to address here, using the Araceae genus Typhonium as a study system. Asian Typhonium have 2n = 10, Australian Typhonium can have 2n = 160, these being the lowest and almost highest numbers in the family. New and published counts also imply a broad range of base chromosome numbers in Typhonium. In a multi-locus phylogeny of Typhonium, the 2n = 10 species are embedded among species with higher chromosome numbers, implying chromosome loss or fusion, while the high counts imply multiple rounds of polyploidization. We propose to investigate (i) karyotype rearrangements that led to chromosome number reduction or multiplication; (ii) genome size changes accompanying chromosome number changes; and (iii) the evolutionary context of changes in genome size and/or chromosome number (for example, time and place, as estimated from the phylogeny). Techniques to be used are molecular phylogenetics, genome size measurements, and fluorescence in situ hybridization (FISH) with repetitive DNA sequences. Pilot FISH data, using material from our large collection of cultivated Typhonium, demonstrate the suitability of Typhonium as a system for genome evolution.