The driving process for the evolutionay trajectory towards C4 photosynthesis

Abstract

Compared to the plants with C3 photosynthesis, the plants with C4 photosynthesis have higher light, water, and nitrogen use efficiencies. Though only 3% of higher plants have C4 photosynthesis, C4 photosynthesis contribute 23% of terrestrial gross primary productivity. However, it remains elusive how the procedure for the evolutionary trajectory from C3 towards C4 photosynthesis is driven. Here, Flaveria genus, the model for C4 evolutionary researches, was used to study the driving procedure through a combined analysis of eco-physiological, biochemical and anatomical data. From proto-Kranz to C4-like, results showed that precipitation was negatively associated with the activity of C4 metabolic core enzyme and C4 flux, respectively. An increased temperature and precipitation which was concurrent with increased vein density were observed during the earlier evolutionary stage. Then, decreased precipitation and increased temperature accompanied the emergence of C2 photosynthesis and further transition from C2 to developing C4 photosynthesis. There was a positive relationship between CO2 compensation point, stomata density and precipitation, suggesting decreasing precipitation enhance photorespiration through closing stomata during evolution. As the driving force from proto-Kranz to C4-like, drought is more important than heat during C4 evolution. This study indicated that the stages during the evolution towards C4 photosynthesis required different driving force and increased water availability should be needed in the initial phase.