Development and Plasticity of Photosynthesis in Sugarcane

The C₄-photosynthesis pathway was discovered in sugarcane. In all C₄-species PEP carboxylase (PEPC) is the primary enzyme of CO₂ fixation. The product of PEPC, oxaloacetate (C₄ - organic acid) is then shuttled to the bundle sheath cells where CO₂ is released from the C₄ - acid via a decarboxylation reaction. There are three different pathways through which this shuttling and decarboxylation can occur and plants are classified based on the dominant pathway. Historically sugarcane has been classified as a NADPME type although the early work indicated that at least 25% of the initial fixed CO₂ is in aspartate and that the NADME pathway is present. This view of a 3:1 ratio between the two pathways has gone unchallenged since its initial discovery. In maize all three types are present but attempts to measure PEPCK in sugarcane failed. We have used annotated transcriptome data to reconstruct the carbon fixation pathways, light reactions and mitochondrial pathways in sugarcane leaves at different stages of development and stress. All three C4 decarboxylation types are present, are not rigidly determined and allow flexibility between the pathways under different physiological conditions.