A Malus Crabapple Chalcone Synthase Gene, McCHS, Regulates Red Petal Color and Flavonoid Biosynthesis

Chalcone synthase is a key and often rate-limiting enzyme in the biosynthesis of anthocyanin pigments that accumulate in plant organs such as flowers and fruits, but the relationship between CHS expression and the petal coloration level in different cultivars is still unclear. In this study, three typical crabapple cultivars were chosen based on different petal colors and coloration patterns. The two extreme color cultivars, ‘Royalty’ and ‘Flame’, have dark red and white petals respectively, while the intermediate cultivar ‘Radiant’ has pink petals. We detected the flavoniods accumulation and the expression levels of McCHS during petals expansion process in different cultivars. The results showed McCHS have their special expression patterns in each tested cultivars, and is responsible for the red coloration and color variation in crabapple petals, especially for color fade process in ‘Radiant’. Furthermore, tobacco plants constitutively expressing McCHS displayed a higher anthocyanins accumulation and a deeper red petal color compared with control untransformed lines. Moreover, the expression levels of several anthocyanin biosynthetic genes were higher in the transgenic McCHS overexpressing tobacco lines than in the control plants. A close relationship was observed between the expression of McCHS and the transcription factors McMYB4 and McMYB5 during petals development in different crabapple cultivars, suggesting that the expression of McCHS was regulated by these transcription factors. We conclude that the endogenous McCHS gene is a critical factor in the regulation of anthocyanin biosynthesis during petal coloration in Malus crabapple.查尔酮合酶（Chalcone synthase）是可在花朵、果实等植物器官中积累的花青素类色素生物合成途径中的关键且常为限速的酶，但CHS的表达水平与不同栽培品种花瓣着色程度之间的关联仍不明确。本研究选取了3个具有不同花瓣颜色和着色模式的典型苹果属海棠（Malus crabapple）栽培品种。其中，两个极端色泽品种‘王族’（Royalty）和‘火焰’（Flame）分别具有深红色与白色花瓣，中间型品种‘绚丽’（Radiant）的花瓣呈粉红色。我们检测了不同品种海棠花瓣发育过程中的类黄酮积累量以及McCHS的表达水平，结果显示McCHS在各供试品种中均具有独特的表达模式，且与海棠花瓣的红色着色及色泽变异密切相关，尤其参与了‘绚丽’品种的花瓣褪色过程。此外，组成型表达McCHS的烟草植株相较于未转化的对照株系，表现出更高的花青素积累量与更深的红色花瓣色泽；同时，转基因过表达McCHS的烟草株系中，多个花青素生物合成相关基因的表达水平均高于对照植株。在不同海棠栽培品种的花瓣发育进程中，McCHS的表达与转录因子McMYB4、McMYB5呈现紧密关联，提示McCHS的表达受到这些转录因子的调控。综上，内源McCHS基因是调控苹果属海棠花瓣着色过程中花青素生物合成的关键因子。