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

泛热带分布且物种丰富的花椒属（芸香科）多倍体和无融合生殖的进化

• 批准号: 451351171
• 负责人: Dr. Marc Appelhans
• 金额: --
• 依托单位: Abteilung Systematik, Biodiversität und Evolution der Planzen
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/451351171?language=en
• 关键词: Evolution; polyploidy; apomixis; pantropically; distributed

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.

该项目的主要目标是研究植物花椒属（芸香科）多倍体和无融合生殖（通过种子进行无性生殖）的进化。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条染色体的古多倍体，但几个温带和夏威夷物种的染色体计数表明具有多达144条染色体的八倍体细胞型。无融合生殖已被记录的几个温带物种，这些物种中的大多数是八倍体。迄今为止，关于花椒属植物的倍性水平和无融合生殖的研究，大多偏向于少数温带种，对无融合生殖体的生殖方式也没有充分的描述。在拟议的研究中，我将生成核型数据（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发芽实验尽可能多的物种描述繁殖模式。为了将这些数据与花椒属的进化历史联系起来，我将根据高通量测序（HTS）数据生成一个详细的系统发育。我将应用HTS方法目标富集（TE），并在一项试点研究中建立了花椒的方法，在该研究中，我为该属设计了一套定制的TE诱饵。一个很好的解决和过时的单倍性将允许确定多倍体和无融合生殖类群的关系，以及确定多倍体化事件的数量和无融合生殖的独立起源。一个更大的分布和更广泛和更极端的生态位相比，有性亲本物种已被描述为一些无融合生殖类群，这种现象已被命名为“地理单性生殖”。我的假设与手头的数据是，所有温带种花椒是无融合生殖和无融合生殖已为温带地区的殖民化和东亚地区的殖民化从温带美洲的祖先的一个必不可少的先决条件。多倍体可能是一个物种内的基因组复制的结果（同源多倍体）或可能与杂交（异源多倍体）。到目前为止，没有杂交类群已被描述为花椒，并研究系统发育不一致的TE序列数据将允许确定是否杂交或其他进化过程，如不完全谱系排序（ILS）发生在属的进化。我的初步研究表明，杂交和ILS可能发生在一些分支。在拟议的项目中，更密集的分类群采样将允许更详细的了解杂交事件的数量，它们的地理和空间起源，以及潜在的亲本分类群的识别。