Most land plants photosynthesize using the ancestral C3 pathway, in which ribulose bisphosphate carboxylase/oxygenase (Rubisco) fixes CO2 into 3-carbon acids in mesophyll cells. The derived C4 pathway, in which a carbon concentrating mechanism operates in the context of specialized leaf anatomy, is more efficient than the C3 pathway. Introduction of the C4 pathway into the C3 crop rice (Oryza sativa) could increase yield by 50% and expression of five C4 enzymes from maize previously led to flux through the first step in transgenic rice. However, there was no evidence for flux later in the cycle. Here we developed new transgenic lines and novel protocols to detect C4 cycle activity against a background of C3 photosynthesis and leaf anatomy. Significantly, we demonstrate that the three core C4 reactions and CO2 refixation are operating in transgenic C3 plants, establishing the in vivo flux framework needed to progress towards a functional carbon-concentrating mechanism.
Baccolini, C. et al. · CC-BY 4.0