State Key Laboratory of Tree Genetics and Breeding, Research Institute of Subtropical Forestry, Chinese Academy of Forestry, Hangzhou, 311400, Zhejiang, China.
College of Information Science and Technology, Nanjing Forestry University, Nanjing, 210037, China.
BMC Biol. 2024 Feb 27;22(1):50. doi: 10.1186/s12915-024-01851-y.
The formation and domestication of ornamental traits are influenced by various aspects, such as the recognition of esthetic values and cultural traditions. Camellia japonica is widely appreciated and domesticated around the world mainly due to its rich variations in ornamental traits. Ornamental camellias have a diverse range of resources, including different bud variations from Camellia spp. as well as inter- and intra- specific hybridization. Despite research on the formation of ornamental traits, a basic understanding of their genetics and genomics is still lacking.
Here, we report the chromosomal-level reference genome of C. japonica through combining multiple DNA-sequencing technologies and obtain a high-density genetic linkage map of 4255 markers by sequencing 98 interspecific F hybrids between C. japonica and C. chekiangoleosa. We identify two whole-genome duplication events in C. japonica: one is a shared ancient γ event, and the other is revealed to be specific to genus Camellia. Based on the micro-collinearity analysis, we find large-scale segmental duplication of chromosome 8, resulting to two copies of the AGAMOUS loci, which may play a key role in the domestication of floral shapes. To explore the regulatory mechanisms of seasonal flowering, we have analyzed year-round gene expression patterns of C. japonica and C. azalea-a sister plant of continuous flowering that has been widely used for cross breeding. Through comparative analyses of gene co-expression networks and annual gene expression patterns, we show that annual expression rhythms of some important regulators of seasonal growth and development, including GIGANTEA and CONSTANS of the photoperiod pathway, have been disrupted in C. azalea. Furthermore, we reveal that the distinctive expression patterns of FLOWERING LOCUS T can be correlated with the seasonal activities of flowering and flushing. We demonstrate that the regulatory module involved in GIGANTEA, CONSTANS, and FLOWERING LOCUS T is central to achieve seasonality.
Through the genomic and comparative genomics characterizations of ornamental Camellia spp., we propose that duplication of chromosomal segments as well as the establishment of gene expression patterns has played a key role in the formation of ornamental traits (e.g., flower shape, flowering time). This work provides a valuable genomic platform for understanding the molecular basis of ornamental traits.
观赏性状的形成和驯化受审美价值观和文化传统等多方面的影响。山茶花在世界各地广泛受到赞赏和驯化，主要是因为其观赏性状的丰富变化。观赏茶花具有多样化的资源，包括不同的茶花品种的芽变以及种间和种内杂交。尽管对观赏性状的形成进行了研究，但对其遗传和基因组学的基本了解仍然缺乏。
在这里，我们通过结合多种 DNA 测序技术报告了山茶花的染色体水平参考基因组，并通过对 98 个山茶花和浙江红花油茶的种间 F1 杂种进行测序，获得了 4255 个标记的高密度遗传连锁图谱。我们在山茶花中鉴定出两个全基因组复制事件：一个是共享的古老γ事件，另一个是特定于山茶属的事件。基于微共线性分析，我们发现 8 号染色体的大规模片段重复，导致 AGAMOUS 基因座的两个拷贝，这可能在花形驯化中发挥关键作用。为了探索季节性开花的调控机制，我们分析了山茶花和连续开花的姊妹植物杜鹃的全年基因表达模式。通过对基因共表达网络和年度基因表达模式的比较分析，我们表明，一些重要的季节性生长和发育调节剂的年度表达节律，包括光周期途径中的 GIGANTEA 和 CONSTANS，在杜鹃中已经被打乱。此外，我们揭示了开花和发叶季节性活动与 FLOWERING LOCUS T 独特表达模式之间的相关性。我们证明，涉及 GIGANTEA、CONSTANS 和 FLOWERING LOCUS T 的调控模块是实现季节性的核心。
通过对观赏山茶属植物的基因组和比较基因组学特征分析，我们提出，染色体片段的重复以及基因表达模式的建立在观赏性状（如花形、开花时间）的形成中发挥了关键作用。这项工作为理解观赏性状的分子基础提供了有价值的基因组平台。
