Computational analysis of two-cell genome scale rice (Oryza sativa) metabolic model overexpressing key NADP-ME C4 pathway enzymes via constraints-based modelling

C4 photosynthesis is a metabolic phenotype characterized by a carbon-concentration mechanism, and is identified as a major target for the improvement of C3 crops such as rice. Recent results on the development of partial C4 rice, however, show only marginal gains in terms of yield. A constraints-based modelling framework was used to analyze the properties of expressing key C4 genes under the context of a predominant C3 phenotye. A two-cell model was constructed and parametrized using an extant one-cell reconstruction of rice metabolism, and was subjected to iterative curation and refinement. Sensitivity analysis for Photon Input, NH4 input as well as CO2 input was performed as well as flux sampling at three different light points. Results have demonstrated that the model mainly showcases a C3 form of photosynthesis but marginal to no gains in terms of photo-assimilate generation efficiency under sub-saturating light conditions. Analysis also reveals that the effect of increasing flux towards key C4 enzymes shows minor effect toward key photosynthesis but marginal to no gains in terms of photo-assimilate generation efficiency under sub-saturating light conditions. Analysis also reveals that the effect of increasing flux towards key C4 enzymes shows minor effect towards key photosynthetic pathways while mainly affecting fluxes in mainly involving dicarboxylate metabolism, including pathways such as Nitrogen Metabolism, the TCA cycle and Amino acid-related reactions. Lastly, authors were able to deduce that the suboptimal fluxes observed for Stromal malate metabolism was mainly limited to NADPH supply as well as the supply of key reducing intermediates in the stroma. This study, in turn, identifies potential routes for the optimization of C4-inducing fluxes for the purpose of the gradual introduction of the C4 phenotype into C3 rice.