Yellow flowers generated by expression of the aurone biosynthetic pathway
Yellow flowers generated by expression of the aurone biosynthetic pathway
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DOI：
10.1073/pnas.0604246103
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发表时间：
2006-07-18
影响因子：
11.1
通讯作者：
Tanaka, Yoshikazu
中科院分区：
文献类型：
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作者：
Ono, Eiichiro;Fukuchi-Mizutani, Masako;Tanaka, Yoshikazu
花的颜色通常由有色的类黄酮色素赋予。橙酮类黄酮赋予金鱼草（金鱼草）和大丽花（大丽花）明亮的黄色。A. majus aureusidin synthase（AmAS 1）是催化查尔酮合成橙酮的关键酶，但过表达AmAS 1基因的转基因花不能合成橙酮。在这里，我们报告，查耳酮4 '-O-葡萄糖基转移酶（4' CGT）是必需的橙酮生物合成和黄色在体内。Am4'CGT和AmAS 1基因的共表达足以使金霉素6-O-葡萄糖苷在转基因蓝猪耳花（Torenia hybrida）中积累。此外，它们的共表达结合通过RNA干扰（RNAi）下调花青素苷的生物合成导致黄花。Am4'CGT-GFP嵌合蛋白定位于细胞质中，而AmAS 1（N1-60）-RFP嵌合蛋白定位于液泡中。因此，我们得出结论，查耳酮在细胞质中被4 '-O-葡萄糖基化，它们的4'-O-葡萄糖苷被运输到液泡中，并在其中酶促转化为橙酮6-O-葡萄糖苷。这种代谢途径在已知的类黄酮例子中是独特的，包括花青素的生物合成，因为对于所有其他化合物，碳骨架在运输到液泡之前完成。我们的研究结果不仅证明了橙酮生物合成的生化基础，而且为缺乏这种颜色变体的主要观赏物种工程黄色花朵开辟了道路。
Flower color is most often conferred by colored flavonoid pigments. Aurone flavonoids confer a bright yellow color on flowers such as snapdragon (Antirrhinum majus) and dahlia (Dahlia variabilis). A. majus aureusidin synthase (AmAS1) was identified as the key enzyme that catalyzes aurone biosynthesis from chalcones, but transgenic flowers overexpressing AmAS1 gene failed to produce aurones. Here, we report that chalcone 4'-O-glucosyltransferase (4'CGT) is essential for aurone biosynthesis and yellow coloration in vivo. Coexpression of the Am4'CGT and AmAS1 genes was sufficient for the accumulation of aureusidin 6-O-glucoside in transgenic flowers (Torenia hybrida). Furthermore, their coexpression combined with down-regulation of anthocyanin biosynthesis by RNA interference (RNAi) resulted in yellow flowers. An Am4'CGT-GFP chimeric protein localized in the cytoplasm, whereas the AmAS1(N1-60)-RFP chimeric protein was localized to the vacuole. We therefore conclude that chalcones are 4'-O-glucosylated in the cytoplasm, their 4'-O-glucosides transported to the vacuole, and therein enzymatically converted to aurone 6-O-glucosides. This metabolic pathway is unique among the known examples of flavonoid, including anthocyanin biosynthesis because, for all other compounds, the carbon backbone is completed before transport to the vacuole. Our findings herein not only demonstrate the biochemical basis of aurone biosynthesis but also open the way to engineering yellow flowers for major ornamental species lacking this color variant.