A leaf-level biochemical model simulating the introduction of C and C photosynthesis in C rice: gains, losses and metabolite fluxes.

This work aims at developing an adequate theoretical basis for comparing assimilation of the ancestral C pathway with CO concentrating mechanisms (CCM) that have evolved to reduce photorespiratory yield losses. We present a novel model for C , C , C  + C and C photosynthesis simulating assimilatory metabolism, energetics and metabolite traffic at the leaf level. It integrates a mechanistic description of light reactions to simulate ATP and NADPH production, and a variable engagement of cyclic electron flow. The analytical solutions are compact and thus suitable for larger scale simulations. Inputs were derived with a comprehensive gas-exchange experiment. We show trade-offs in the operation of C that are in line with ecophysiological data. C has the potential to increase assimilation over C at high temperatures and light intensities, but this benefit is reversed under low temperatures and light. We apply the model to simulate the introduction of progressively complex levels of CCM into C rice, which feeds > 3.5 billion people. Increasing assimilation will require considerable modifications such as expressing the NAD(P)H Dehydrogenase-like complex and upregulating cyclic electron flow, enlarging the bundle sheath, and expressing suitable transporters to allow adequate metabolite traffic. The simpler C rice may be a desirable alternative.