Beijing Key Laboratory of Ornamental Plants Germplasm Innovation & Molecular Breeding, Beijing, 100083, China; National Engineering Research Center for Floriculture, Beijing, 100083, China; Beijing Laboratory of Urban and Rural Ecological Environment, Beijing, 100083, China; College of Landscape Architecture, Beijing Forestry University, Beijing, 100083, China.
Beijing Key Laboratory of Ornamental Plants Germplasm Innovation & Molecular Breeding, Beijing, 100083, China; National Engineering Research Center for Floriculture, Beijing, 100083, China; Beijing Laboratory of Urban and Rural Ecological Environment, Beijing, 100083, China; College of Landscape Architecture, Beijing Forestry University, Beijing, 100083, China.
Plant Physiol Biochem. 2019 Sep;142:415-428. doi: 10.1016/j.plaphy.2019.07.023. Epub 2019 Aug 2.
The variation of flower color of chrysanthemum (Chrysanthemum×morifolium) is extremely rich, and carotenoids, which are mainly stored in the plastid, are important pigments that determine the color of chrysanthemum. However, the genetic regulation of the carotenoid metabolism pathway in this species still remains unclear. In this study, a pink chrysanthemum cultivar, 'Jianliuxiang Pink', and its three bud sport mutants (including white, yellow and red color mutants, 'Jianliuxiang White', 'Jianliuxiang Yellow' and 'Jianliuxiang Red', respectively) were used as experimental materials to analyze the dynamic changes of carotenoid components and plastid ultrastructure at different developmental stages of ray florets. We found that the carotenoid components and plastid ultrastructure of the four color cultivars in the early developmental stage of the chrysanthemum capitulum (S1) were almost identical, and the carotenoids mainly included violaxanthin, lutein and β-carotene, which exist in proplastids and immature chloroplasts. With the development of capitulum, the chloroplasts in 'Jianliuxiang White' and 'Jianliuxiang Pink' were degraded, and the protoplasts did not transform but rather formed vesicles that accumulated trace amounts of carotenoids. The proplastids and chloroplasts in 'Jianliuxiang Yellow' and 'Jianliuxiang Red' were all transformed into chromoplasts and consist of lutein as well as lutein's isomer and derivatives. Using comparative transcriptomics combined with gene expression analysis, we found that CmPg-1, CmPAP10, and CmPAP13, which were involved in chromoplast transformation, CmLCYE, which was involved in carotenoid biosynthesis, and CmCCD4a-2, which was involved in carotenoid degradation, were differentially expressed between four cultivars, and these key genes therefore should affect the accumulation of carotenoids in chrysanthemum. In addition, six transcription factors, CmMYB305, CmMYB29, CmRAD3, CmbZIP61, CmAGL24, CmNAC1, were screened using weighted gene co-expression correlation network analysis (WGCNA) combined with correlative analysis to determine whether they play an important role in carotenoid accumulation by regulating structural genes related to the carotenoid metabolism pathway and plastid development. This study analyzed dynamic changes of carotenoid components and plastid ultrastructure of the four bud mutation cultivars of chrysanthemum and identified structural genes and transcription factors that may be involved in carotenoid accumulation. The above results laid a solid foundation for further analysis of the regulatory mechanism of the carotenoid biosynthesis pathway in chrysanthemum.
菊花（Chrysanthemum×morifolium）花色变异极其丰富，主要储存在质体中的类胡萝卜素是决定菊花花色的重要色素。然而，该物种中类胡萝卜素代谢途径的遗传调控仍不清楚。本研究以粉色菊花品种‘剑流香粉’及其三个芽变突变体（包括白色、黄色和红色花色突变体，分别为‘剑流香白’、‘剑流香黄’和‘剑流香红’）为实验材料，分析了不同发育阶段舌状花花蕾中类胡萝卜素成分和质体超微结构的动态变化。我们发现，四个花色品种在菊花头状花序早期发育阶段（S1）的类胡萝卜素成分和质体超微结构几乎相同，类胡萝卜素主要包括紫黄质、叶黄素和β-胡萝卜素，存在于前质体和未成熟的叶绿体中。随着头状花序的发育，‘剑流香白’和‘剑流香粉’的叶绿体降解，质体没有转化，而是形成了含有痕量类胡萝卜素的小泡。‘剑流香黄’和‘剑流香红’的前质体和叶绿体均转化为有色体，由叶黄素以及叶黄素的异构体和衍生物组成。通过比较转录组学结合基因表达分析，我们发现，参与有色体转化的 CmPg-1、CmPAP10 和 CmPAP13、参与类胡萝卜素生物合成的 CmLCYE 以及参与类胡萝卜素降解的 CmCCD4a-2 在四个品种之间存在差异表达，这些关键基因因此可能影响菊花中类胡萝卜素的积累。此外，使用加权基因共表达网络分析（WGCNA）结合相关性分析筛选了六个转录因子，包括 CmMYB305、CmMYB29、CmRAD3、CmbZIP61、CmAGL24 和 CmNAC1，以确定它们是否通过调节与类胡萝卜素代谢途径和质体发育相关的结构基因来调控花色突变体中类胡萝卜素的积累。本研究分析了菊花四个芽变突变体的类胡萝卜素成分和质体超微结构的动态变化，鉴定了可能参与类胡萝卜素积累的结构基因和转录因子。上述结果为进一步分析菊花类胡萝卜素生物合成途径的调控机制奠定了基础。
