We investigated the bi-colored dahlia cultivar ‘Seattle’, which exhibits bright yellow petals with white tips, for its potential use as a model system for studies of the anthochlor biosynthesis. The yellow base contained high amounts of the 6′-deoxychalcones and the structurally related 4-deoxyaurones, as well as flavones. In contrast, only traces of anthochlors and flavones were detected in the white tips. No anthocyanins, flavonols, flavanones or dihydroflavonols were found in the petals. Gene expression studies indicated that the absence of anthocyanins in the petals is caused by a lack of flavanone 3-hydroxylase (FHT) expression, which is accompanied by a lack of expression of the bHLH transcription factor IVS. Expression of other genes involved in anthocyanidin biosynthesis such as dihydroflavonol 4-reductase (DFR) and anthocyanidin synthase (ANS) was not affected. The yellow and white petal parts showed significant differences in the expression of chalcone synthase 2 (CHS2), which is sufficient to explain the absence of yellow pigments in the white tips. Transcriptomes of both petal parts were de novo assembled and three candidate genes for chalcone reductase (CHR) were identified. None of them showed a significantly higher expression in the yellow base compared to the white tips. In summary, it was shown that the bicolouration is most likely caused by a bottleneck in chalcone formation in the white tip. The relative prevalence of flavones compared to the anthochlors in the white tips could be an indication for the presence of a so far unknown differentially expressed CHR.

我们研究了双色的大丽花栽培品种“西雅图”，它表现出亮黄色的花瓣和白色的尖端，因为它有潜力用作研究邻氯甲烷生物合成的模型系统。黄色碱含有大量的6'-脱氧查耳酮和与结构相关的4-脱氧金龙酮以及黄酮。相反，在白色针头中仅检测到痕量的草毒和黄酮。在花瓣中未发现花青素，黄酮醇，黄烷酮或二氢黄酮醇。基因表达研究表明，花瓣中花色苷的缺乏是由于缺乏黄烷酮3-羟化酶（FHT）的表达所引起的，其同时伴随着bHLH转录因子IVS的缺乏表达。不影响其他花青素生物合成相关基因的表达，例如二氢黄酮醇4-还原酶（DFR）和花青素合酶（ANS）。黄色和白色的花瓣部分在查尔酮合酶2（CHS2）的表达中显示出显着差异，这足以解释白色尖端中不存在黄色颜料。从头开始组装两个花瓣部分的转录组，并建立了查尔酮还原酶（CHR）的三个候选基因被确定。与白色针尖相比，它们在黄色碱基中均未显示出明显更高的表达。总而言之，显示出双色是最可能由白色尖端中查尔酮形成的瓶颈引起的。黄酮与邻氯苯酚在白头中的相对患病率可能是迄今为止未知的差异表达CHR的征兆。