Carotenoid Analysis of a Liverwort Marchantia polymorpha and Functional Identification of its Lycopene β- and ε-Cyclase Genes

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 β-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 β-cyclase (LCYb) and lycopene ε-cyclase (LCYe), which were involved in the synthesis of β-carotene and α-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 β-carotene from lycopene, which was the same as that of higher plants. On the other hand, liverwort LCYe was able to form two ε-rings from lycopene to ε-carotene via δ-carotene, which was different from the Arabidopsis LCYe enzyme which generates only one ε-ring from lycopene.