Evolution of polyploidy and apomixis in the pantropically distributed and species-rich genus Zanthoxylum (Rutaceae)

该项目的主要目标是研究花椒属植物的多倍体和无融合生殖的进化，即通过种子进行无性繁殖。花椒是一个物种丰富的属，广泛分布于所有热带地区以及北美和东亚的温带地区。虽然大多数物种似乎是具有72-80条染色体的古代多倍体，但一些温带和夏威夷物种的染色体计数表明，它是一种八倍体细胞型，最多有144条染色体。几个温带物种的无融合生殖已经被记录下来，这些物种中的大多数是八倍体。到目前为止，关于花椒倍性水平和无融合生殖的研究偏向于少数温带物种，对无融合生殖方式的描述还不够充分。在拟议的研究中，我将生成核学数据(染色体计数、使用流式细胞术和其他方法的倍性估计)，并通过显微镜研究和对尽可能多的物种进行萌发实验来描述繁殖模式。为了将这些数据与花椒的进化史联系起来，我将根据高通量测序(HTS)数据生成详细的系统发育图。我将应用HTS方法目标浓缩(TE)，并在一项初步研究中建立了花椒的方法，在该研究中，我为花椒属设计了定制的TE诱饵集。一个明确的和过时的系统发育将允许确定多倍体和无融合生殖分类群的关系，以及确定多倍化事件的数量和无融合生殖的独立起源。与有性亲本物种相比，许多无融合生殖类群的分布范围更广，生态位更广和更极端，这种现象被称为地理孤雌生殖。我的假设是，所有温带的花椒物种都是无融合生殖的，无融合生殖是温带地区和温带美洲祖先在东亚地区殖民的必要先决条件。多倍体可能是一个物种内基因组复制的结果(同源多倍体)，也可能与杂交(异源多倍体)有关。到目前为止，还没有描述花椒的杂交分类群，研究TE序列中的系统发育不一致性将有助于确定在该属的进化过程中是否发生了杂交或其他进化过程，如不完全谱系排序(ILS)。我的初步研究表明，杂交和ILS可能发生在一些分支中。拟议项目中更密集的分类群采样将使人们能够更详细地了解杂交事件的数量、它们的地理和空间来源，以及识别潜在的亲本分类群。

The main goal of the proposed project is to study the evolution of polyploidy and apomixis, asexual reproduction via seeds, in the plant genus Zanthoxylum (Rutaceae). Zanthoxylum is a species-rich genus with a wide distribution in all tropical regions plus temperate areas in North America and East Asia. While most species seem to be paleopolyploids with 72-80 chromosomes, chromosome counts of several temperate and Hawaiian species suggest an octaploid cytotype with up to 144 chromosomes. Apomixis has been documented for several temperate species and most of these species are octaploid. So far, there is a large bias towards the few temperate species in the studies about ploidy levels and apomixis in Zanthoxylum and the mode of reproduction in apomicts has not been described sufficiently. Within the proposed study, I will generate karyological data (chromosome counts, ploidy estimations using Flow Cytometry and other methods) and describe the mode of reproduction via microscopic studies and germination experiments for as many species as possible. In order to link this data with the evolutionary history of Zanthoxylum, I will generate a detailed phylogeny based on High-Throughput Sequencing (HTS) data. I will apply the HTS method Target Enrichment (TE) and have established the method for Zanthoxylum in a pilot study in which I designed a custom TE bait set for the genus. A well-resolved and dated phylogeny will allow to determine the relationships of polyploid and apomictic taxa as well as to determine the numbers of polyploidization events and independent origins of apomictic reproduction. A larger distribution and a wider and more extreme ecological niche compared to the sexual parental species has been described for a number of apomictic taxa and this phenomenon has been named “geographical parthenogenesis”. My hypothesis with the data at hand is that all temperate species of Zanthoxylum are apomicts and that apomixis has been an essential prerequisite for the colonization of temperate regions and for the colonization of East Asian regions from a temperate American ancestor.Polyploidy may be the result of genome duplication within a species (autopolyploidy) or may be linked to hybridization (allopolyploidy). So far, no hybrid taxa have been described for Zanthoxylum, and studying phylogenetic incongruences in the TE sequence data will allow to determine if hybridization or other evolutionary processes such as Incomplete Lineage Sorting (ILS) have taken place in the evolution of the genus. My pilot study indicated that hybridization and ILS might have occurred in some clades. The denser taxon sampling in the proposed project will allow more detailed insights about the number of hybridization events, their geographical and spatial origins, and the identification of potential parental taxa.