Chionanthus retusus, an arbor tree of the Oleaceae family, is an ecologically and economically valuable ornamental plant for its remarkable adaptability in landscaping. During C. retusus breeding, we observed diverse floral shapes; however, no available genome for C. retusus has hindered the widespread identification of genes related to flower morphology. Thus, a de novo telomere-to-telomere (T2T) gap-free genome was generated. The assembly, incorporating high-coverage and long-read sequencing data, successfully yielded two complete haplotypes (687 and 683 Mb). The genome encompasses 42 864 predicted protein-coding genes, with all 46 telomeres and 23 centromeres in one haplotype. Whole genome duplication analysis revealed that C. retusus underwent one fewer event of whole-genome duplication after differentiation compared to other species in the Oleaceae family. Furthermore, flower vein diversity was the main reason for the differences in floral shapes. Auxin-related genes were responsible for petal shape formation on genome-based transcriptome analysis. Specifically, the removal and retention of the first intron in CrAUX/IAA20 resulted in the production of two transcripts, and the differences in the expression levels of CrAUX/IAA20 resulted in the variations of flower veins. Compared to transcripts lacking the first intron, transcripts with intron retention caused more severe decreases in the number and length of flower veins in transgenic Arabidopsis thaliana. Our findings will deepen our understanding of flower morphology development and provide important theoretical support for the cultivation of Oleaceae.

中文翻译：

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Chionanthus retusus 的端粒到端粒无间隙参考基因组提供了对花瓣形状变化的分子机制的见解


Chionanthus retusus 是木犀科乔木树种，因其在园林绿化中的适应性而成为一种具有生态和经济价值的观赏植物。在C. retusus 育种过程中，我们观察到了不同的花形；然而，没有可用的 C. retusus 基因组阻碍了与花形态相关的基因的广泛鉴定。因此，从头生成端粒到端粒（T2T）无间隙基因组。该组装结合了高覆盖率和长读长的测序数据，成功产生了两个完整的单倍型（687 和 683 Mb）。该基因组包含 42 864 个预测的蛋白质编码基因，其中所有 46 个端粒和 23 个着丝粒都位于一种单倍型中。全基因组复制分析表明，与木犀科的其他物种相比，C. retusus 在分化后经历的全基因组复制事件较少。此外，花脉多样性是造成花形差异的主要原因。在基于基因组的转录组分析中，生长素相关基因负责花瓣形状的形成。具体来说，CrAUX/IAA20中第一个内含子的去除和保留导致了两个转录本的产生，而CrAUX/IAA20表达水平的差异导致了花脉的变异。与缺乏第一个内含子的转录本相比，保留内含子的转录本导致转基因拟南芥中花脉的数量和长度更严重地减少。我们的研究结果将加深我们对花卉形态发育的认识，并为木犀科植物的栽培提供重要的理论支持。