A leaf‐level biochemical model simulating the introduction of C₂ and C₄ photosynthesis in C₃ rice: gains, losses and metabolite fluxes

Abstract

Summary This work aims at developing an adequate theoretical basis for comparing assimilation of the ancestral C3 pathway with CO2 concentrating mechanisms (CCM) that have evolved to reduce photorespiratory yield losses. We present a novel model for C3, C2, C2 + C4 and C4 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 C4 that are in line with ecophysiological data. C4 has the potential to increase assimilation over C3 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 C3 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 C2 rice may be a desirable alternative.

On the road to C4 rice: advances and perspectives

“…The concept of C 4 rice has excited photosynthetic modellers and there are a number of photosynthetic models that have tried to evaluate the efficacy of introducing C 4 photosynthesis into rice (Bellasio, ; Yin and Struik, ; Wang et al , ; Bellasio and Farquhar, ). Each of these models has a different focus.…”

Ensuring Nutritious Food Under Elevated CO2 Conditions: A Case for Improved C4 Crops

“…Recently, Lundgren (2020) presented a compelling case for engineering C 2 photosynthesis into C 3 crop plants to improve photosynthetic performance in the face of climate change. The main argument made in favor of this approach is that C 2 photosynthesis is a stable intermediate physiological state between C 3 and C 4 metabolism that increases net carbon assimilation under high temperatures ( Monson, 1989 ; Bellasio and Farquhar, 2019 ). But, importantly, C 2 photosynthesis does not require the complex anatomical changes associated with C 4 photosynthesis ( Lundgren, 2020 ).…”

C2 photosynthesis: a promising route towards crop improvement?

“…They found that, compared to traditional C 3 rice, C 2 rice assimilated more carbon under ambient CO 2 conditions, but also across a broad environmental space including warm temperatures (c. > 35°C), high light (c. > 700 µmol m À2 s À1 ), and low CO 2 concentrations (c. < 400 µmol mol À1 ). Moreover, C 2 photosynthesis conveys such strong benefits under warm temperatures that even in the high CO 2 concentrations predicted under climate change scenarios, C 2 rice will outpace C 3 rice in terms of carbon assimilation above c. 35°C (Bellasio & Farquhar, 2019).…”