Carotenoid analysis of a liverwort Marchantia polymorpha and functional identification of its lycopene beta - and epsilon -cyclase genes.

摘要

Carotenoid biosynthesis in bryophytes has yet to be clarified. The liverwort Marchantia polymorpha L. is known to be an early land plant and is an emerging bryophyte model. In order to gain insight into the evolution of carotenoid biosynthesis in plants, we studied carotenoid biosynthesis in this liverwort. As is the case in higher plants, liverwort thalli contain lutein and beta -carotene, as major carotenoids, as well as zeaxanthin, antheraxanthin, violaxanthin and 9'-cis-neoxanthin. Based on liverwort expressed sequence tag (EST)/cDNA and genome sequences, we isolated two cyclase genes encoding lycopene beta -cyclase (LCYb) and lycopene epsilon -cyclase (LCYe), which were involved in the synthesis of beta -carotene and alpha -carotene. These enzymes were phylogenetically positioned between corresponding proteins of a green alga (Chlorophyta) and higher plants. Functional analysis of the two genes was performed using a heterologous Escherichia coli expression system, in which the Pantoea ananatis lycopene biosynthesis genes were co-expressed. The results indicated liverwort LCYb activity for the synthesis of beta -carotene from lycopene, which was the same as that of higher plants. On the other hand, liverwort LCYe was able to form two epsilon -rings from lycopene to epsilon -carotene via delta -carotene, which was different from the Arabidopsis LCYe enzyme which generates only one epsilon -ring from lycopene.