The prasinophytes encompass a number of basal lineages of green algae (Chlorophyta) that significantly contribute to marine primary productivity and thus are important components of the marine food web. Most prasinophytes belong to the picoplankton and are characterized by tiny cells with compact genomes. Nevertheless, their carotenoid composition is far more complex than that of other green algae. By taking advantage of available genome data we have identified various genes potentially involved in the biosynthesis of this carotenoid diversity and now are in the process of functional characterization of the corresponding gene products.
As a recent example, we have characterized a fusion protein from the prasinophyte Ostreococcus lucimarinus consisting of a lycopene-epsilon-cyclase, a lycopene-beta-cyclase and a C-terminal light-harvesting complex (LHC) domain. Expression of the fusion protein in lycopene-accumulating E. coli resulted in the formation of both alpha- and beta-carotene. Removal of the LHC domain and gradual truncation of the linker peptide altered the ratio of alpha- and beta-carotene, suggesting that the LHC domain controls the access of the substrate lycopene to the two lycopene cyclase domains. This may represent a novel mechanism for adjusting the biosynthetic ratio of alpha- and beta-carotenoids during photoacclimation of the algae.
Palenik et al. (2007), Blatt et al. (2015)