Increasing Rubisco as a simple means to enhance photosynthesis and productivity now without lowering nitrogen use efficiency

Abstract

Global demand for food may rise by 60% mid-century. A central challenge is to meet this need using less land in a changing climate. Nearly all crop carbon is assimilated through Rubisco, which is catalytically slow, reactive with oxygen, and a major component of leaf nitrogen. Developing more efficient forms of Rubisco, or engineering CO₂ concentrating mechanisms into C₃ crops to competitively repress oxygenation, are major endeavors, which could hugely increase photosynthetic productivity (≥ 60%). New technologies are bringing this closer, but improvements remain in the discovery phase and have not been reduced to practice. A simpler shorter-term strategy that could fill this time gap, but with smaller productivity increases (c. 10%) is to increase leaf Rubisco content. This has been demonstrated in initial field trials, improving the productivity of C₃ and C₄ crops. Combining three-dimensional leaf canopies with metabolic models infers that a 20% increase in Rubisco increases canopy photosynthesis by 14% in sugarcane (C₄) and 9% in soybean (C₃). This is consistent with observed productivity increases in rice, maize, sorghum and sugarcane. Upregulation of Rubisco is calculated not to require more nitrogen per unit yield and although achieved transgenically to date, might be achieved using gene editing to produce transgene-free gain of function mutations or using breeding.

Keywords: C3 photosynthesis; C4 photosynthesis; Rubisco; food security; future‐proofing agriculture; global change; nitrogen use efficiency; rising CO2.

Fig. 1

Average yields of wheat and sorghum over the last 60 yr. (a) Average wheat yields reported for France, Germany and the UK; and (b) average World sorghum yields. Yield refers to the harvested production per hectare for the area under cultivation. Official figures reported from 1961 to 2022 (FAOstat, 2024).

Fig. 2

Effect of a 20% increase in Rubisco on A to C _i response curves in soybean (C₃) and sorghum (C₄). (a) ‘Wild‐type’ (WT) shows the modeled leaf CO₂ uptake (A) vs intercellular CO₂ concentration (C _i) using the V _c,max and J _max reported for soybean accession PI561370 (Montes et al., 2022) as inputs to the FvCB equations (von Caemmerer, 2013). The effect of increasing Rubisco activity by 20% is represented by ‘V _c,max × 1.2’ and of increasing both Rubisco and capacity for RuBP regeneration by 20% by ‘V _c,max and J _max × 1.2’. Vertical dashed lines assume an operating C _i, which is 0.7 of C _a, where C _a in 2050 is estimated as c. 500 μmol mol⁻¹. (b) ‘WT’ represents the measured mean A to C _i of sorghum line RTx430 compared to three independent lines of the same background, but with a transgenic upregulation of Rubisco of c. 25% (Salesse‐Smith et al., 2024). Vertical dashed lines represent the operating C _i of the past present and future, assuming a C _i, which is 0.4 of C _a.

Fig. 3

Enhancement of canopy CO₂ assimilation rates in sugarcane from a 20% increase in Rubisco. (a) ‘Wild‐type’ (WT) shows the modeled diurnal crop photosynthetic CO₂ uptake as described previously for a mature sugarcane canopy in the present atmosphere (Wang et al., 2017). The effect of increasing Rubisco activity by 20% is represented by ‘V _c,max × 1.2’. The percent increase in CO₂ uptake is integrated over the day relative to ‘WT’. (b) The enhancement of leaf net CO₂ assimilation from additional 20% Rubisco (ΔA) in a modeled sugarcane canopy (Saccharum officinarum, RB86‐7515) at 12:00 h on 20 July, Sao Paulo, Brazil. The row spacing of the canopy is 100 cm. Leaf area index is 5.8. Colors indicate the spatial heterogeneity of the change in A throughout the canopy at 12:00 h.

Fig. 4

Enhancement of canopy CO₂ assimilation rates in soybean from a 20% increase in Rubisco. (a) ‘Wild type’ (WT) shows the modeled diurnal crop photosynthetic CO₂ uptake as described previously for a mature soybean canopy in the present atmosphere (Wang et al., 2020). The effect of increasing Rubisco activity by 20% is represented by V _c,max × 1.2 and of increasing both Rubisco and capacity for RuBP regeneration by V _c,max and J _max × 1.2. The percent increase in CO₂ uptake integrated over the day relative to ‘WT’. (b) As for (a) but at a future atmospheric [CO₂] of 500 μmol mol⁻¹. (c) The enhancement of leaf net CO₂ assimilation from additional 20% Rubisco (ΔA) in a modeled soybean canopy (Glycine max L. Merr., LD11‐2170) at 12:00 h on 18 August, Champaign, IL, USA. The atmospheric [CO₂] is 400 μmol mol⁻¹, the row spacing of the canopy is 76 cm, and plant spacing within the rows 5 cm. Leaf area index is 5.9. Colors indicate the spatial heterogeneity of the change in A throughout the canopy at 12:00 h.