Can the Cyanobacterial Carbon-Concentrating Mechanism Increase Photosynthesis in Crop Species? A Theoretical Analysis    

Abstract

Experimental elevation of [CO 2 ] around C 3 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 C 3 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 C 3 leaf are unexamined. Here, a CO 2 and HCO 3 2 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 2 transporters, as a single HCO 3 2 transporter increased modeled A sat by 9%. Addition of all major CCM components increased A sat from 24 to 38 mmol m 22 s 21 . 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.

pH determines the energetic efficiency of the cyanobacterial CO 2 concentrating mechanism

“…Here, we identify the cell membrane permeability to HCO 3 − as a key parameter determining leakage. All previous models of the CCM tracked only HCO 3 − , implicitly ignoring other species of hydrated Ci (H 2 CO 3 , HCO 3 − , and CO 3 2− , which we collectively term H total ) and their contribution to cell permeability (14)(15)(16)(17)(18)(19). This implicit assumption is at odds with biochemical intuition that charge is a major determinant of membrane permeability (20).…”

Meeting the Global Food Demand of the Future by Engineering Crop Photosynthesis and Yield Potential

“…Not only can the metabolic pathways and their cellular organization be represented in silico, but there is now the opportunity to integrate them into realistic representations of the whole canopy of a crop, facilitating predictions of optimal distribution of resources at the sub-cellular, cellular, leaf, and whole-crop level (Drewry et al, 2014;Song et al, 2013;Tholen et al, 2012;Tholen and Zhu, 2011). HPC allows the in silico investigation of thousands of permutations of up-and downregulation of the genes and proteins involved in photosynthesis, or the impacts of the potential addition of foreign genes and pathways, to identify the best targets for practical manipulation (McGrath and Long, 2014;Xin et al, 2015). Finally, the third factor is the advance in genetic engineering.…”

Surveying Rubisco diversity and temperature response to improve crop photosynthetic efficiency

“…If combined with complimentary changes such as optimizing other components of the Calvin Benson or photorespiratory cycles (Raines, 2011;Peterhansel et al, 2013;Simkin et al, 2015), optimized canopy architecture (Drewry et al, 2014), or introducing elements of a carbon concentrating mechanism (Furbank et al, 2009;Lin et al, 2014a;Hanson et al, 2016;Long et al, 2016), Rubisco improvement presents an opportunity to dramatically increase the photosynthetic efficiency of crop plants (McGrath and Long, 2014;Long et al, 2015;Betti et al, 2016). A combination of the available strategies is essential for devising tailored solutions to meet the varied requirements of different crops and the diverse conditions under which they are typically grown around the world.…”