Pu Ya, Huang He, Wen Xiaohui, Lu Chenfei, Zhang Bohan, Gu Xueqi, Qi Shuai, Fan Guangxun, Wang Wenkui, Dai Silan
Beijing Advanced Innovation Center for Tree Breeding by Molecular Design, Beijing Key Laboratory of Ornamental Plants Germplasm Innovation & Molecular Breeding, National Engineering Research Center for Floriculture, Beijing Laboratory of Urban and Rural Ecological Environment, Key Laboratory of Genetics and Breeding in Forest Trees and Ornamental Plants of Education Ministry, School of Landscape Architecture, Beijing Forestry University, Beijing, 100083, China.
Fuzhou Planning Design & Research Institute, Fuzhou, 350108, China.
BMC Genomics. 2020 Oct 20;21(1):728. doi: 10.1186/s12864-020-07110-y.
The ray floret shapes referred to as petal types on the chrysanthemum (Chrysanthemum × morifolium Ramat.) capitulum is extremely abundant, which is one of the most important ornamental traits of chrysanthemum. However, the regulatory mechanisms of different ray floret shapes are still unknown. C. vestitum is a major origin species of cultivated chrysanthemum and has flat, spoon, and tubular type of ray florets which are the three basic petal types of chrysanthemum. Therefore, it is an ideal model material for studying ray floret morphogenesis in chrysanthemum. Here, using morphological, gene expression and transcriptomic analyses of different ray floret types of C. vestitum, we explored the developmental processes and underlying regulatory networks of ray florets.
The formation of the flat type was due to stagnation of its dorsal petal primordium, while the petal primordium of the tubular type had an intact ring shape. Morphological differences between the two ray floret types occurred during the initial stage with vigorous cell division. Analysis of genes related to flower development showed that CYCLOIDEA genes, including CYC2b, CYC2d, CYC2e, and CYC2f, were differentially expressed in different ray floret types, while the transcriptional levels of others, such as MADS-box genes, were not significantly different. Hormone-related genes, including SMALL AUXIN UPREGULATED RNA (SAUR), GRETCHEN HAGEN3 (GH3), GIBBERELLIN 2-BETA-DIOXYGENASE 1 (GA2OX1) and APETALA2/ETHYLENE RESPONSIVE FACTOR (AP2/ERF), were identified from 1532 differentially expressed genes (DEGs) in pairwise comparisons among the flat, spoon, and tubular types, with significantly higher expression in the tubular type than that in the flat type and potential involvement in the morphogenesis of different ray floret types.
Our findings, together with the gene interactional relationships reported for Arabidopsis thaliana, suggest that hormone-related genes are highly expressed in the tubular type, promoting petal cell division and leading to the formation of a complete ring of the petal primordium. These results provide novel insights into the morphological variation of ray floret of chrysanthemum.
菊花（Chrysanthemum × morifolium Ramat.）头状花序上被称为花瓣类型的舌状花形态极为丰富，这是菊花最重要的观赏性状之一。然而，不同舌状花形态的调控机制仍不清楚。野菊（C. vestitum）是栽培菊花的主要起源物种，具有平瓣、匙瓣和管瓣三种菊花基本花瓣类型的舌状花。因此，它是研究菊花舌状花形态发生的理想模式材料。在此，我们通过对野菊不同舌状花类型进行形态学、基因表达和转录组分析，探索了舌状花的发育过程及其潜在调控网络。
平瓣类型的形成是由于其背面花瓣原基停滞发育，而管瓣类型的花瓣原基呈完整的环状。两种舌状花类型之间的形态差异在细胞分裂旺盛的初始阶段就已出现。对花发育相关基因的分析表明，CYCLOIDEA基因，包括CYC2b、CYC2d、CYC2e和CYC2f，在不同舌状花类型中差异表达，而其他基因如MADS-box基因的转录水平无显著差异。从小勺瓣、平瓣和管瓣两两比较得到的1532个差异表达基因（DEG）中鉴定出激素相关基因，包括小生长素上调RNA（SAUR）、GRETCHEN HAGEN3（GH3）、赤霉素2-β-双加氧酶1（GA2OX1）和APETALA2/乙烯响应因子（AP2/ERF），这些基因在管瓣类型中的表达显著高于平瓣类型，并可能参与不同舌状花类型的形态发生。
我们的研究结果，结合拟南芥中报道的基因相互作用关系，表明激素相关基因在管瓣类型中高表达，促进花瓣细胞分裂并导致花瓣原基形成完整的环状。这些结果为菊花舌状花形态变异提供了新的见解。
