Abstract
Bougainvillea has large and vibrant-colored bracts, which are widely used in landscape gardening. In order to study the changing pattern of pigmentation and the expression of genes related to pigment synthesis during different developmental periods of the bracts of B. × buttiana, we determined the color parameters of the bracts of B. × buttiana has by using colorimetric color cards and colorimeters, and quantitatively determined the contents of chlorophyll a, chlorophyll b, betacyanin, betaxanthin and flavonoids, and the expression of genes related to pigment synthesis was detected during the BR1 and BR3. The results showed that the bracts of B. × buttiana 'Miss Manila' can be classified into four distinct growth and developmental stages, namely Bract Primordial Stage (BR1), Bract Color Transition Stage (BR2), Bract Maturation Stage (BR3), and Bract Senescence Stage (BR4). The BR1 have lower color saturation, brightness, and redness, and with bract development, their color saturation, brightness, and redness gradually increased. In addition, chlorophyll content was highest at the BR1 (2.2 mg/g), and from the BR1, flavonoids and betalain content began to increase, and higher betacyanin content in all stages, with betacyanin being the highest at the BR3 at 4.94 mg/g. Correlation analysis of the color parameters with pigment content showed that chlorophyll a, betacyanin, and flavonoid contents were significantly correlated with the bract color changes. With bract development, the betalain metabolism pathway BgDODA gene was significantly up-regulated; the flavonoid metabolism pathway BgDFRA and BgF3H genes were significantly up-regulated, whereas the BgDTX, BgFLS, and BgCHIL genes were significantly down-regulated; and the chlorophyll metabolism pathway BgSGR gene was significantly up-regulated, whereas the BgPORA gene was down-regulated in expression. ProtParam-based analysis characterized the BgFLS-encoded protein as a stable, hydrophilic 2-oxoglutarate-dependent oxidoreductase lacking transmembrane domains and a signal peptide, and the BgCHIL-encoded protein as a stable, hydrophilic chalcone isomerase also lacking transmembrane domains and a signal peptide. In summary, betalain metabolism, flavonoid metabolism and chlorophyll metabolism jointly regulate the bract color change of B. × buttiana has, and it is possible that the genes of BgCHIL, BgFLS, BgSGR, and BgF3H are involved in the regulation of the bract color change of B. × buttiana.