温度对桂花花瓣主要呈色物质类胡萝卜素代谢的调控机制

Osmanthus fragrans is one of the important landscape plants in China. Composition and content of carotenoids are the major factors determining petal coloration of O. fragrans. The change of ambient temperature could have a significant impact on petal coloration of different color O. fragrans cultivars, which greatly affects the ornamental value of O. fragrans in autumn. Previous studies found that the regulation of temperature change on the carotenoids content in petals directly impacts on petal coloration of O. fragrans. However, at present, little information is available on the molecular mechanism of temperature regulating petal color of O. fragrans. In this study, different color O. fragrans cultivars will be employed as materials to research the effects of different temperature conditions on petal color, composition and content of major carotenoids, the expression of carotenoids biosynthesis and carotenoids degradation genes involved in carotenoids metabolism pathway. Based on the analysis of the relation among gene expression, petal color and carotenoids accumulation, the key genes involved in temperature-regulated carotenoids biosynthesis will be identified. Then, further studies on the biological function of these key genes will be carried out, as well as the isolation of the promoters of the key genes and the response mechanism of promoters to different temperature conditions. Our study could reveal the regulatory mechanism of temperature on the metabolism of carotenoids, the major coloring factor, in the petal of O. fragrans, which will have important practical significance to improve petal color and other ornamental traits using environmental factors and provide theoretical foundation for molecular breeding of petal color in O. fragrans.

桂花是我国重要的园林植物之一。类胡萝卜素的种类和含量是决定桂花花色呈现的最主要因素。环境温度的变化对不同花色品种桂花花瓣的呈色产生显著影响，桂花秋季的观赏价值因此大打折扣。前期研究发现，温度变化对花瓣类胡萝卜素含量的调控将直接影响到桂花花瓣的呈色，但是目前温度调控桂花花色的分子机理不清楚。本研究拟以桂花不同花色品种为试验材料，研究不同温度条件对桂花花色、主要类胡萝卜素种类和含量以及类胡萝卜素代谢途径中合成和降解相关基因表达的影响，分析相关基因表达和花色、类胡萝卜素积累之间的关系，筛选响应温度调控桂花类胡萝卜素合成的关键基因。然后对关键基因的生物学功能进行研究，同时分离关键基因的启动子，并研究其对不同温度条件的响应机理。本研究将解析温度对桂花花瓣主要呈色物质类胡萝卜素代谢的调控机制，为利用环境因子改善桂花花色和其他观赏性状产生重要的实际意义，也为桂花花色分子育种提供理论依据。

环境温度对不同花色品种桂花花瓣的呈色产生作用,进而影响桂花的观赏价值。本研究以不同花色秋桂品种‘玉玲珑’、‘金球桂’和‘堰虹桂’为研究材料，相对于对照（19℃），高温（32℃）处理条件下，不同品种花瓣花色变淡，花色明度L*值增加、红度a*值和彩度C*值下降；低温（12和15℃）处理条件下，不同品种花瓣花色变深，花色明度L*值下降、红度a*值和彩度C*值增加。利用HPLC法对不同处理桂花花瓣类胡萝卜素成分进行定量分析发现，高温处理降低类胡萝卜素含量，特别是α-胡萝卜素和β-胡萝卜素的含量；而低温处理显著增加α-胡萝卜素和β-胡萝卜素的含量，进而提高花瓣中类胡萝卜素总量。利用荧光定量PCR法测定不同温度处理条件下花瓣中类胡萝卜素代谢相关基因的表达，发现低温促进部分合成基因的表达，尤其是OfLCYB1基因，其表达量在低温条件下明显上调；而高温能诱导OfCCD1等类胡萝卜素降解基因的高丰度表达，由此筛选得到OfLCYB1基因和OfCCD1基因为响应温度变化调控的类胡萝卜素合成及降解的关键基因。然后，对关键基因启动子序列进行分离，得到1028 bp OfLCYB1启动子序列，以及2个OfCCD1基因的启动子序列CCD1P-L和CCD1P-S，其序列长度分别为2747 bp和981 bp。OfLCYB1基因和OfCCD1基因的启动子序列均含有脱落酸等多种激素信号响应元件，推测环境温度通过激素信号转导途径调控OfLCYB1基因和OfCCD1基因的表达，进而影响桂花花瓣类胡萝卜素的积累和呈色。