Improving Light Use Efficiency in C₄ Plants by Increasing Electron Transport Rate

Abstract

C4 plants play a key role in world agriculture and strategies to manipulate and enhance C4 photosynthesis have the potential for major agricultural impacts. The C4 photosynthetic pathway is a biochemical CO2 concentrating mechanism that requires the coordinated functioning of mesophyll and bundle sheath cells of leaves. Chloroplast electron transport in C4 plants is shared between the two cell types; it provides resources for CO2 fixation therefore underpinning the efficiency of photosynthesis. Using the model monocot C4 species Setaria viridis (green foxtail millet) we demonstrated that the Cytochrome (Cyt) b6f complex regulates the electron transport capacity and thus the rate of CO2 assimilation at high light and saturating CO2. Overexpression of the Cyt b6f in both mesophyll and bundle sheath cells results in a higher electron throughput and allows better light conversion efficiency in both photosystems. Importantly, increased Cyt b6f abundance in leaves provides higher rates of C4 photosynthesis without marked changes in Rubisco or chlorophyll content. Our results demonstrate that increasing the rate of electron transport is a viable strategy for improving the light conversion efficiency in C4 crop species like maize and sorghum.

Keywords

• C₄ photosynthesis
• electron transport
• biotechnology
• light harvesting