Aureusidin synthase: A polyphenol oxidase homolog responsible for flower coloration

Aurones are plant flavonoids that provide yellow color to the flowers of so me popular ornamental plants, such as snapdragon and cosmos. In this study, we have identified an enzyme responsible for the synthesis of aurone from chalcones in the yellow snapdragon flower, The enzyme (aureusidin synthase) is a 39-kilodalton, copper-containing glycoprotein catalyzing the hydroxyl ation and/or oxidative cyclization of the precursor chalcones, 2',4',6',4-t etrahydroxychalcone and 2',4',6',3,4-pentahydroxychalcone. The complementar y DNA encoding aureusidin synthase is expressed in the petals of aurone-con taining varieties, DNA sequence analysis revealed that aureusidin synthase belongs to the plant polyphenol oxidase family, providing an unequivocal ex ample of the function of the polyphenol oxidase homolog in plants, i.e., fl ower coloration.