第1050回生物科学セミナー
The Evolution of C4 Photosynthesis in Higher Plants.
Professor Rowan F. Sage（Dept of Ecology and Evolutionary Biology, University of Toronto）
2015年05月28日(木) 17:00-18:45 理学部 2号館 講堂
The C4 pathway is a complex trait, with dozens to hundreds of genetic modifications during its origin. How, when and why the C4 pathway evolved have been major questions in photosynthetic biology since its discovery in the 1960’s. The recent addition of phylogenetic approaches to the study of C4 plants has led to significant advances in our understanding of their origins. Among the leading advances are the discovery that the C4 pathway has independently evolved over 65 times, making it one of the most prolific of evolutionary phenomenon in the biosphere. Molecular clock analyses now show that C4 plants first evolved with the reduction in the Earth’s atmospheric CO2 level beginning in the late Oligocene epoch some 30 million years ago. Subsequent origins of the C4 pathway are spread over recent geological time, with numerous origins occurring in the past 5 million years. Physiological, ecological and molecular evidence indicates high levels of photorespiration are the main selection agent during C4 evolution, with low CO2, heat, drought, and harsh soils (particularly sandy, rocky, or saline soils) combining to create high rates of photorespiration in C3 species and hence strong selection pressures that lead to C4 photosynthesis. A key development that facilitates the rise of C4 photosynthesis is the formation of a two-tissue photorespiratory pathway, in which photorespiratory metabolites must travel between mesophyll and bundle sheath cells to be fully metabolized. This two-celled pathway occurs because the expression of the photorespiratory enzyme glycine decarboxylase becomes localized into mitochondria of bundle sheath cells. This development initiates a series of structural and biochemical changes that subsequently facilitates the origin of the C4 biochemistry. The ability to form the two-celled photorespiratory pathway is thus considered a key initial hurdle in C4 evolution. In addition to reviewing evidence for the above advances, this seminar will evaluate hypotheses of how C4 evolution is first initiated in C3 ancestral species.
Additional Reading:
Sage RF, PA Christin, EJ Edwards. 2011. The C4 plant lineages of planet Earth. Journal of Experimental Botany 62:3155-3169.
Sage RF, TL Sage, F Kocacinar. 2012. Photorespiration and the evolution of C4 photosynthesis. Annual Review of Plant Biology 63:19-47.
Sage TL, FA Busch, DC Johnson, PC Friesen, CR Stinson, M Stata, S Sultmanis, BA Rahman, S Rawsthorne, RF Sage. 2013. Initial events during the evolution of C4 photosynthesis in C3 species of Flaveria. Plant Physiology 163:1266–1276.
Sage RF, R Khoshravesh, TL Sage. 2014. From proto-Kranz to C4 Kranz: Building the bridge to C4 photosynthesis. Journal of Experimental Botany 65:3341-3356.
