Isolation and Characterization of a Lycopene ε-Cyclase Gene of Chlorella (Chromochloris) zofingiensis. Regulation of the Carotenogenic Pathway by Nitrogen and Light

The isolation and characterization of the lycopene epsilon-cyclase gene from the green microalga Chlorella (Chromochloris) zofingiensis (Czlcy-e) was performed. This gene is involved in the formation of the carotenoids alpha-carotene and lutein. Czlcy-e gene encoded a polypeptide of 654 amino acids. A single copy of Czlcy-e was found in C. zofingiensis. Functional analysis by heterologous complementation in Escherichia coli showed the ability of this protein to convert lycopene to delta-carotene. In addition, the regulation of the carotenogenic pathway by light and nitrogen was also studied in C. zofingiensis. High irradiance stress did not increase mRNA levels of neither lycopene beta-cyclase gene (lcy-b) nor lycopene epsilon-cyclase gene (lcy-e) as compared with low irradiance conditions, whereas the transcript levels of psy, pds, chyB and bkt genes were enhanced, nevertheless triggering the synthesis of the secondary carotenoids astaxanthin, canthaxanthin and zeaxanthin and decreasing the levels of the primary carotenoids alpha-carotene, lutein, violaxanthin and beta-carotene. Nitrogen starvation per se enhanced mRNA levels of all genes considered, except lcy-e and pds, but did not trigger the synthesis of astaxanthin, canthaxanthin nor zeaxanthin. The combined effect of both high light and nitrogen starvation stresses enhanced significantly the accumulation of these carotenoids as well as the transcript levels of bkt gene, as compared with the effect of only high irradiance stress.