Diversity and evolution of photosynthetic antenna systems in green plants

Photosynthetic antenna systems are mainly involved in the absorption of light energy required for photosynthesis. The typical green plants arrange chlorophylls a and b and carotenoids, including lutein and 9'-cis neoxanthin, in their antenna systems; such antenna systems have prospered on earth. Therefore, these antenna systems should be highly evolved and should adapt to the photoenvironments in which plants grow. However, little information is available on the diversity and evolution of antenna systems in green plants as a whole. To approach this, the present study focused on the antenna systems in the Prasinophyceae, an assemblage of early diverging lineages of green plants and analyzed their photosynthetic pigments in detail. In the present study, various novel blue-green light-absorbing siphonaxanthin series were detected in the early diverging species of the Prasinophyceae and the distribution of these carotenoids was revealed. Additionally, to clarify the evolution of antenna systems in the Ulvophyceae, a highly developed green algal group that specializes in inhabiting various aquatic environments, members of the Cladophorales belonging to this class were selected and their carotenoid compositions were determined to compare them with the molecular phylogenetic tree constructed on the basis of the 18S rRNA gene sequences of the Cladophorales. In this review, these data will be summarized and the remarkable variation of photosynthetic pigments will be presented. A possible scenario detailing the evolution of antenna systems in green plants will be elucidated.