Structural diversity and functional novelty of new carotenoid biosynthesis genes.

Many new carotenoid synthesis genes have recently been identified through genomic sequencing or functional cloning. Some of them exhibit novel structures and/or novel functions. This review describes such examples in the families of lycopene β-cyclases, putative homologues of phytoene dehydrogenases and new carotenoid hydroxylases. Both the functionally novel lycopene β-monocyclases and structurally novel fusion-type of lycopene β-cyclases were described. Another newly discovered sequence of lycopene β-cyclase described might represent a new class of lycopene β-cyclases previously not identified in several cyanobacteria. Three examples of putative homologues of phytoene dehydrogenases were described, however, they were confirmed to encode different and/or new functions such as β-carotene ketolase, 4,4′-diapolycopene oxygenase or prolycopene isomerase. Two new carotenoid hydroxylase genes were described that encoded the new function of 2,2′-β-ionone ring hydroxylase or 3,3′-isorenieratene hydroxylase. Phylogenetic analysis of these genes shed light on their possible evolutionary origins. These new genes also provide tools for synthesis of novel and desirable carotenoids by genetic engineering.