Yellow flowers: Take two

Researchers who thought they understood how some yellow flowers get their color were led down the garden path, but now they have the story straight. Flowers such as snapdragon and dahlia obtain their yellow color from aurone flavonoids (bottom, Glc = glucose) derived from chalcones (top, R = H). Chalcones can also be converted into anthocyanins, which range from blue to red. Eiichiro Ono of Japan's Suntory Ltd. and colleagues genetically engineered blue flowering plants to make aureusidin synthase, the enzyme they thought was responsible for the production of aurones. Unexpectedly, the plants failed to make any aurones (Proc. Natl. Acad. Sci. USA 2006, 103, 11075). The researchers discovered that another enzyme—chalcone 4′-O-glucosyltransferase— first adds glucose to the chalcone molecule. Aureusidin synthase then converts this intermediate (top, R = glucose) into the yellow pigment. The researchers produced yellow blooms in plants that lack this color by introducing genes for both enzymes into the plants while using RNA interference to suppress anthocyanin biosynthesis.