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Juric, I; Hibberd, JM; Blatt, M; Burroughs, NJ (2019) Computational modelling predicts substantial carbon assimilation gains for C-3 plants with a single-celled C-4 biochemical pump. PLoS Comp Bio. 15 10.1371/journal.pcbi.1007373

Juric, I; Hibberd, JM; Blatt, M; Burroughs, NJ (2019) Computational modelling predicts substantial carbon assimilation gains for C-3 plants with a single-celled C-4 biochemical pump. PLoS Comp Bio. 15 10.1371/journal.pcbi.1007373

Achieving global food security for the estimated 9 billion people by 2050 is a major scientific challenge. Crop productivity is fundamentally restricted by the rate of fixation of atmospheric carbon. The dedicated enzyme, RubisCO, has a low turnover and poor specificity for CO2. This limitation of C-3 photosynthesis (the basic carbon-assimilation pathway present in all plants) is alleviated in some lineages by use of carbon-concentrating-mechanisms, such as the C-4 cycle-a biochemical pump that concentrates CO2 near RubisCO increasing assimilation efficacy. Most crops use only C-3 photosynthesis, so one promising research strategy to boost their productivity focuses on introducing a C-4 cycle. The simplest proposal is to use the cycle to concentrate CO2 inside individual chloroplasts. The photosynthetic efficiency would then depend on the leakage of CO2 out of a chloroplast. We examine this proposal with a 3D spatial model of carbon and oxygen diffusion and C-4 photosynthetic biochemistry inside a typical C-3-plant mesophyll cell geometry. We find that the cost-efficiency of C-4 photosynthesis depends on the gas permeability of the chloroplast envelope, the C-4 pathway having higher quantum efficiency than C-3 for permeabilities below 300 mu m/s. However, at higher permeabilities the C-4 pathway still provides a substantial boost to carbon assimilation with only a moderate decrease in efficiency. The gains would be capped by the ability of chloroplasts to harvest light, but even under realistic light regimes a 100% boost to carbon assimilation is possible. This could be achieved in conjunction with lower investment in chloroplasts if their cell surface coverage is also reduced. Incorporation of this C-4 cycle into C-3 crops could thus promote higher growth rates and better drought resistance in dry, high-sunlight climates.

Thu 31 Oct 2019, 10:10