Photocontrol of chs gene expression in petunia flowers

In the present work we studied the effect of light and diurnal light-dark periods on the expression of the anthocyanin biosynthetic gene, chalcone synthase (chs), in petunia corollas. We found that light is essential for chs expression at the early stages of flower development. At these stages chs transcript level fluctuated during the day-night cycles. Our results also showed that the fluctuation is regulated by the diurnal light signal and not by an endogenous clock. The effect of the light was cumulative and thus chs mRNA reached maximum levels at the end of the diurnal light period. At later stages of flower development, when chs transcript is rapidly accumulated, expression was only slightly affected by light and did not fluctuate during the diurnal light-dark period. We suggest that the low sensitivity of ohs expression to external signals at the later stages of flower development is essential to ensuring normal flower coloration under changing environmental conditions.