Photosynthesis research on yellowtops: Macroevolution in progress

The vast majority of angiosperms, including most of the agronomically important crop plants (wheat, etc.), assimilate CO2 through the inefficient C-3 pathway of photosynthesis. Under ambient conditions these organisms loose about 1/3 of fixed carbon via photorespiration, an energetically wasteful process. Plants With C-4 photosynthesis (such as maize) eliminate photorespiration via a biochemical CO2-pump and thus have a larger rate of carbon gain. The genus Flaveria (yellowtops, Asteraceae) contains not only C-3 and C-4 species, but also many C-3-C-4 intermediates, which have been interpreted as evolving from C-3 to fully expressed C-4 metabolism. However, the evolutionary significance Of C-3-C-4 Flaveria-intermediates has long been a matter of debate. A well-resolved phylogeny of nearly all Flaveria species has recently been published. Here, we review pertinent background information and combine this novel phylogeny with physiological data. We conclude that the Flaveria species complex provides a robust model system for the study of the transition from C-3 to C-4 photosynthesis, which is arguably a macroevolutionary event. We conclude with comments relevant to the current Intelligent Design debate. (C) 2006 Elsevier GmbH. All rights reserved.