Origin and evolution of apomixis in North American Boechera species, Brassicaceae

美洲十字花科Boechera属(前身为Arabis)，形成一个定义明确的单系分类群，以北美西部为中心，有80种。该属的进化被认为是由网状和无融合生殖驱动的。后者在十字花科中是独一无二的，并与极低的倍性水平(主要是二倍体或三倍体)有关，这使牛膝成为理想的遗传研究系统。此外，已有研究表明B染色体与无融合生殖有关。关于无融合生殖性状的进化，DNA序列数据表明，在非整倍体和三倍体的Boechera holboellii中，严格羊草(=Arabis drummondii)是基因组增加的来源。拟议的项目将主要侧重于无融合生殖特征的起源、传递和分类分布及其对该属物种形成和多样化的影响。为此目的，在先前集中于三个模式物种的研究中获得的对进化机制的洞察将被作为起点，它们是有性的、无融合生殖的、有性的和无融合生殖的Boechera holboellii及其杂交的Boechera divaricarpa。该项目的目的是：(I)发展基于叶绿体和核DNA的北美羊草属的系统发育，以了解多倍体、无融合生殖和非整倍体在空间和时间上的分布和传播方式；(Ii)分别鉴定与杂交起源物种组成有关的古代基因类型；(Iii)显示B染色体的分类分布，并验证它们是否在无融合生殖的建立中起普遍作用；(Iv)区分物种的单系和多系起源，(5)核实落基山脉作为主要多样性中心和内华达山脉作为次要多样性中心在整个属一级的重要性。

The American genus Boechera (formerly Arabis), Brassicaceae, froms a well-defined monophyletic taxon with 80 species centered in Western North America. Evolution of the genus is thought to have been driven by reticulation and apomixis. Latter trait is unique within the Brassicaceae and associated with exceptionally low ploidy levels (mostly diploid or triploid), which makes Boechera an ideal genetic study system. Furthermore, it has been shown that B chromosomes are associated with apomixis. Regarding evolution of the apomictic trait, DNA sequence data suggested Boechera stricta (= Arabis drummondii) as the origin of genome addition in aneuploid and triploid Boechera holboellii. The proposed project will mainly focus on the origin, transmission and taxonomic distribution of the apomictic trait and its consequences for the speciation and diversification of the genus. For this purpose, insights into evolutionary mechanisms gained during previous research efforts concentrating on three model species, sexual Boechera stricta (= Arabis drummondii), sexual and apomictic Boechera holboellii, and their hybrid Boechera divaricarpa, will be used as starting point. The aim of the proposed project is (i) to develop chloroplast and nuclear DNA based phylogenies of North American genus Boechera, in order to understand the distribution and modes of transmission, respectively, of polyploidy, apomixis and aneuploidy in a spatial and temporal context, (ii) to identifiy taxa, respectively, ancient genotypes involved in the consitution of species of hybrid origin, (iii) to show the taxonomic distribution of B chromosomes, and to verify, if they play universal role in the establishment of apomixis, (iv) to distinguish between monophyletic and polyphyletic origin of species, (v) to verify the importance of the Rocky Mountains as primary and the Sierra Nevada as secondary center of diversity on a genus wide level.