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

美洲的布氏属（原阿拉伯属），芸苔科，来自一个定义明确的单系分类群，有80种，集中在北美西部。该属的进化被认为是由网状和无融合驱动的。后一性状在芸苔科中是独特的，并且与极低的倍性水平（主要是二倍体或三倍体）相关，这使得Boechera成为一个理想的遗传研究系统。此外，研究表明B染色体与无融合有关。关于非整倍体和三倍体hobohera holboellii非整倍体和三倍体基因组添加的起源，DNA序列数据表明，Boechera stricta （= Arabis drummondii）是无融合性状的进化起源。本项目将重点研究该性状的起源、传播和分类分布及其对该属物种形成和多样性的影响。为了达到这个目的，在之前的研究工作中，对三个模式物种的进化机制的深入研究将作为起点，这三个模式物种是有性的窄腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹圆腹。本项目的目的是：(1)建立基于叶绿体和细胞核DNA的北美Boechera属的系统发育系统，以了解其多倍体、无融合体和非整倍体在时空背景下的分布和传播方式；(2)分别确定与杂交起源物种构成相关的古老基因型分类群；(3)显示B染色体的分类分布，并验证。如果它们在无融合的建立中发挥了普遍作用，（iv）区分物种的单系起源和多系起源，(v)在属水平上验证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.