Can the Cyanobacterial Carbon-Concentrating Mechanism Increase Photosynthesis in Crop Species? A Theoretical Analysis~(1WOPEN)

摘要

Experimental elevation of CO_2 around C3 crops in the field has been shown to increase yields by suppressing the Rubisco oxygenase reaction and, in turn, photorespiration. Bioengineering a cyanobacterial carbon-concentrating mechanism (CCM) into C3 crop species provides a potential means of elevating CO_2 at Rubisco, thereby decreasing photorespiration and increasing photosynthetic efficiency and yield. The cyanobacterial CCM is an attractive alternative relative to other CCMs, because its features do not require anatomical changes to leaf tissue. However, the potential benefits of engineering the entire CCM into a C3 leaf are unexamined. Here, a CO_2 and HCO_3~- diffusion-reaction model is developed to examine how components of the cyanobacterial CCM affect leaf light-saturated CO_2 uptake (A_(sat)) and to determine whether a different Rubisco isoform would perform better in a leaf with a cyanobacterial CCM. The results show that the addition of carboxysomes without other CCM components substantially decreases A_(sat) and that the best first step is the addition of HCO_3~- transporters, as a single HCO_3~- transporter increased modeled A_(sat) by 9. Addition of all major CCM components increased A_(sat) from 24 to 38 μmol m~(-2) s~(-1). Several Rubisco isoforms were compared in the model, and increasing ribulose bisphosphate regeneration rate will allow for further improvements by using a Rubisco isoform adapted to high CO_2. Results from field studies that artificially raise CO_2 suggest that this 60 increase in A_(sat) could result in a 36 to 60 increase in yield.