C4 photosynthesis is ecologically important on a global scale. Despite representing less than 3% of land plant species diversity, C4 plants account for around 25% of global terrestrial primary productivity.¹ C4 plants dominate and define entire biomes, primarily tropical, subtropical, and warm temperate grasslands and savannahs, as well as saltmarshes and disturbed ecosystems.² Because virtually all C4 plants lack arborescence, there are no C4 forests.³ The competitive advantage of C4 photosynthesis in warm and arid regions has been largely responsible for the expansion of many grassland biomes in regions that would otherwise be forests or shrubland.⁴ The rise of C4 grasses to dominance in many parts of the world created new ecological niches promoting animal and plant diversification. There is thus a direct link from C4 photosynthesis to biodiversity.

C4 plants are also important for human society, as some of our most planted and most productive cereal crops are C4 plants - maize, sorghum, sugarcane, and millet. The prospect of engineering the C4 pathway into C3 plants such as rice and soybean could dramatically improve the efficiency of these crops and improve global food security.⁵ There is worldwide interest in such C4 engineering projects (c4rice.com, 3to4.org). Many C4 plants are also being studied or put to use as bioenergy crops in order to reduce our dependence on fossil fuels.⁶ Improved understanding of the evolution and genetic regulation of C4 photosynthesis will better enable humanity to utilize existing C4 crops and potentially improve other crops via C4 engineering.