Integrating phylogeny into studies of C4 variation in the grasses

Abstract

C4 photosynthesis consists of morphological and biochemical novelties that create a CO2 pump that concentrates CO2 around Rubisco (Kanai and Edwards, 1999), which decreases photorespiration and the resulting energy waste. Consequently, C4 photosynthesis provides a competitive advantage in all conditions where photorespiration costs become important, especially at high temperatures and in arid and saline conditions (Sage, 2001). Despite being used by only 3% of extant angiosperm species (Sage, 2004), C4 plants account for one-fifth of global terrestrial primary production (Ehleringer et al., 1997). This is mainly due to the high productivity of C4 monocots, especially C4 grasses, which are the most speciose C4 group (Sage, 2004). The C4 grasses dominate most open subtropical and tropical habitats, and some, such as maize (Zea mays), sorghum (Sorghum bicolor), millets (e.g. Pennisetum glaucum, Setaria italica), and sugarcane (Saccharum officinarum), are used as crops and have direct importance for human food consumption and/or as livestock fodder (Table I).