Faster induction of photosynthesis increases biomass and grain yield in glasshouse-grown transgenic Sorghum bicolor overexpressing Rieske FeS.

Sorghum is one of the most important crops providing food and feed in many of the world's harsher environments. Sorghum utilises the C 4 pathway of photosynthesis in which a biochemical carbon concentrating mechanism results in high CO 2 assimilation rates. Overexpressing the Rieske subunit of the Cytochrome b 6 f complex was previously shown to increase the rate of photosynthetic electron transport and stimulate CO 2 assimilation in the model C 4 plant Setaria viridis. To test whether productivity of C 4 crops could be improved by Rieske overexpression, we created transgenic Sorghum bicolor Tx430 plants with increased Rieske content. The transgenic plants showed no marked changes in abundance of other photosynthetic proteins or chlorophyll content. The steady-state rates of electron transport and CO 2 assimilation did not differ between the plants with increased Rieske abundance and control plants, suggesting that Cytochrome b 6 f is not the only factor limiting electron transport in sorghum at high light and high CO 2 . However, faster responses of non-photochemical quenching as well as an elevated yield of Photosystem II and an increased CO 2 assimilation rate were observed from the plants overexpressing Rieske during the induction, a process of activation of photosynthesis upon the dark-light transition. Sorghum with increased Rieske content could produce more biomass and grain when grow in glasshouse conditions. Our results indicate that increasing Rieske content has potential to boost productivity of sorghum and other C 4 crops by improving the efficiency of light utilisation and conversion to biomass through the faster induction of photosynthesis.