Molecular evolution of lycopene cyclases involved in the formation of carotenoids with ionone end groups

A survey is given of the lycopene cyclase genes present in bacteria, fungi and plants where two completely unrelated types exist. One is the classical monomeric bacterial beta -cyclase gene, crt Y, which may be an ancestor of crtL, the gene for a beta -cyclase in cyanobacteria. From crtL a line of e volution can be drawn to plant beta- and epsilon -cyclase genes and to the gene of capsanthin/capsorubin synthase. In Gram-positive bacteria two genes crtYc and crtYd are present. They encode two proteins which have to intera ct as a heterodimer for lycopene beta -cyclization. From this type of lycop ene cyclase gene the fungal lycopene cyclase/ phytoene synthase fusion gene evolved.