The present invention relates to optimized ketolase coding sequences, corresponding coding sequences and genetic constructs alone or in combination with beta-cyclase coding sequences, their use for the expression in plants, in particular in plants of the genus Tagetes, to such genetically modified plants, to a process for the preparation of carotenoid products by culturing the genetically modified plants. The present invention further relates to the expression of optimized ketolase coding sequences alone or in combination with beta-cyclase coding sequences under control of an Antirrhinum majus ANTHIRRHINUM FIDDLEHEAD (AFI) promoter, In addition the invention relates to the use of an AFI promoter for heterologous gene expression, preferably for flower-specific expression of genes in plants of the genus Tagetes, to the genetically modified plants of the genus Tagetes, and to a process for producing biosynthetic products by cultivating the genetically modified plants.
