Disentangling the complex karyotype evolution of crocuses

异倍体被认为是多倍化后重新二倍化的主要驱动力，它也可能是多样性的驱动力，因为它造成了核型差异，起到生殖障碍的作用。然而，我们对这些过程的了解是基于极少数经过充分调查的例子，而且还缺乏机械性的解释。番红花属非倍体染色体数目的高频率变化在具有单着丝粒染色体的植物中是不寻常的。在极端情况下，基本染色体数量在几百万年内从n=15减少到n=4，同时基因组大小翻了一番。近缘番红花类群的共域和毗邻分布表明，它们不同的染色体数目可能代表着跨越障碍。然而，分子分析已经发现，尽管亲本物种在核型上存在差异，但在一些番红花群体中存在同倍体杂交。因此，有必要进行详细的群体和细胞遗传学分析，以了解不同的核型和染色体数量在生殖隔离中可能发挥的作用，并有助于阐明在染色体水平上起作用的机制。全基因组复制(WGD)被认为是诱发异倍体的原因。因此，对整个属的WGD事件的初步鉴定对于将它们与改变的异倍体频率相关联是至关重要的。然而，仅仅从番红花的染色体数目或基因组大小不能推断多倍化。取而代之的是，我们将使用NGS数据的k-mer频率和相关番红花支系代表的转录组或猎枪序列数据中的同源基因的识别。(I)一旦鉴定出具有WGD事件的分支，我们就可以推断多倍化之后是否发生了异倍体以及多倍化发生的速度有多快，以及单个WGD事件是否触发了多个染色体重排，最终导致了不同物种的染色体数目。(Ii)为了追踪非倍体核型变化，我们将通过在三个选定的藏红花种群中开发和使用染色体景观标记来跟踪染色体/染色体部分的命运。(Iii)将进行平行交叉实验，以推断不同的(非倍体)核型对生殖隔离强度的影响。该项目将揭开番红花复杂的染色体进化，对异倍体在植物进化中的作用提供重要的见解，并旨在建立该属作为单中心植物中非倍性的机制和调节的模式。

Dysploidy is assumed to be a main driver for re-diploidization after polyploidization and it could also be a driver of diversification by creating karyotype differences functioning as reproductive barriers. Our knowledge regarding these processes is, however, based on very few well-investigated examples and mechanistic explanations are yet lacking. The high frequency of dysploid chromosome number changes in the genus Crocus is unusual for plants with monocentric chromosomes. In extreme cases, the basic chromosome number was reduced from n = 15 to n = 4 within a few million years while doubling genome size at the same time. The sympatric and parapatric occurrence of closely related Crocus taxa without morphologically recognizable hybrids suggests that their different chromosome numbers might represent crossing barriers. However, molecular analysis already revealed the presence of homoploid hybridization in some Crocus groups despite parental species differing in their karyotypes. Therefore, in-detail population- and cytogenetic analyses are necessary to understand the role that different karyotypes and chromosome numbers might play in reproductive isolation and will add to clarify what mechanisms act at chromosome level. It is assumed that whole-genome duplication (WGD) triggers dysploidy. Thus, the initial identification of WGD events across the genus is crucial to correlate them with changed dysploidy frequencies. However, polyploidization cannot be deduced from mere chromosome numbers or genome sizes in Crocus. Instead, we will use k-mer frequencies of NGS data and identification of paralogous genes in transcriptome or shotgun sequences data of representatives of the relevant Crocus clades. (i) Once the clades with WGD events in the genus are identified, we can infer if and how fast dysploidy follows polyploidization and if single WGD events trigger multiple chromosomal rearrangements resulting eventually in species with different chromosome numbers.(ii) To trace dysploid karyotype changes, we will follow the fate of chromosomes/chromosome parts through dysploidy events by developing and employing chromosomal landscape markers in three selected species groups of Crocus.(iii) Crossing experiments will be set up in parallel to infer the influence of different (dysploid) karyotypes on the strengths of reproductive isolation or lack thereof. The proposed project will unravel the complex chromosome evolution of crocuses, give important insights in the role of dysploidy in plant evolution, and is aimed to establish the genus as model for mechanisms and regulation of dysploidy in monocentric plants.