Understanding C4 photosynthesis in Setaria by a proteomic and kinetic approach

Plants performing C4 photosynthesis have a higher productivity per crop area related to an optimized use of water and nutrients. This is achieved through a series of anatomical and biochemical features that allow the concentration of CO2 around RuBisCO. In C4 plants the photosynthetic reactions are distributed between two cell types, they initially fix the carbon to C4 acids within the mesophyll cells (M) and then transport these compounds to the bundle sheath cells (BS), where they are decarboxylated so that the resulting CO2 is incorporated into the Calvin cycle (CC). This work is focused on the comparative analysis of the proteins present in M and BS of Setaria viridis, a C4 model close relative of several major feed, fuel, and bioenergy grasses. The integration of kinetic and proteomic approaches agrees that the C4 compound malate is mainly decarboxylated in the chloroplasts of BS cells by NADP-malic enzyme (NADP-ME). Besides, NAD-malic enzyme (NAD-ME) located in the mitochondria could also contribute to the C4 carbon shuttle. We presented evidence of metabolic strategies that involve chloroplastic, mitochondrial and peroxisomal proteins to avoid the leakage of C4 intermediates in order to sustain an efficient photosynthetic performance. HighlightProteomic and kinetic analyses show metabolic strategies involving chloroplastic, mitochondrial and peroxisomal proteins to maintain the C4 cycle performance in parallel to other metabolic pathways.