Resolving the green branch of life: Current progress and future challenges
Yoshii, Yukie .
Diversity and evolution of Chl a/b-binding photosynthetic antenna systems in green plants.
Light-harvesting pigment-protein complexes (LHCs) collect sunlight for photosynthesis and transfer energy to their respective photosystems. LHCs of land plants and chlorophytes contain Chls a and b, and lutein as photosynthetic pigments, which contribute to light harvesting, stabilize the structure of LHC, and protect the photosynthetic apparatus from potentially damaging light. However, little is known about the diversity and evolution of the LHCs in green plants. In the present study, I focused on the antenna systems in the Prasinophyceae, an assemblage of early diverging lineages of green plants. I analyzed photosynthetic pigments in several prasinophytes by HPLC, mass, and NMR analyses. In Mesostigma viride and Pterosperma cristatum, I found various novel siphonaxanthin series, all of which absorb blue-green light. Some other prasinophytes, regarded to be closely related branches to the chlorophytes, contained lutein, a putative photoprotector, whereas they lacked siphonaxanthin series, as is the case in the streptophytes. From these results, I suggest that the blue-green light-absorbing antenna system using siphonaxanthin series was the most ancient antenna system in green plants and that the antenna systems evolved as an adaptation to a high light environment, by replacing the blue-green light-absorbing siphonaxanthin series with lutein. Furthermore, I propose that acquisition of a photoprotection mechanism enabled green plants to expand their habitat from deep aquatic environment to sunny shallow water and eventually, to land. I sequenced the Lhc*mv1 gene for the LHC protein of M. viride. Using the amino acid sequences, I reconstructed hydrophobicity plot and helical wheel diagram of Lhc*mv1. From protein analysis, I suggest that the flexibility of potential carotenoid-binding sites made possible diversification of photosynthetic antenna system in green LHCs.
1 - Institute of Biological Sciences, University of Tsukuba, Tennoudai, 1-1-1, Tsukuba, Ibaraki, 305-8572, Japan
Presentation Type: Symposium
Location: Ballroom 3 (Cliff Lodge)
Date: Wednesday, August 4th, 2004
Time: 11:45 AM