Improving photosynthesis through the enhancement of Rubisco carboxylation capacity

Abstract

Rising human population, along with the reduction in arable land and the impacts of global change, sets out the need for continuously improving agricultural resource use efficiency and crop yield (CY). Bioengineering approaches for photosynthesis optimization have largely demonstrated the potential for enhancing CY. This review is focused on the improvement of Rubisco functioning, which catalyzes the rate-limiting step of CO2 fixation required for plant growth, but also catalyzes the ribulose-bisphosphate oxygenation initiating the carbon and energy wasteful photorespiration pathway. Rubisco carboxylation capacity can be enhanced by engineering the Rubisco large and/or small subunit genes to improve its catalytic traits, or by engineering the mechanisms that provide enhanced Rubisco expression, activation and/or elevated [CO2] around the active sites to favor carboxylation over oxygenation. Recent advances have been made in the expression, assembly and activation of foreign (either natural or mutant) faster and/or more CO2-specific Rubisco versions. Some components of CO2 concentrating mechanisms (CCMs) from bacteria, algae and C4 plants has been successfully expressed in tobacco and rice. Still, none of the transformed plant lines expressing foreign Rubisco versions and/or simplified CCM components were able to grow faster than wild type plants under present atmospheric [CO2] and optimum conditions. However, the results obtained up to date suggest that it might be achievable in the near future. In addition, photosynthetic and yield improvements have already been observed when manipulating Rubisco quantity and activation degree in crops. Therefore, engineering Rubisco carboxylation capacity continues being a promising target for the improvement in photosynthesis and yield.

Here comes the sun: How optimization of photosynthetic light reactions can boost crop yields

“…While the photochemical lightdependent reactions involve harvesting of excitation energy from sunlight to produce the energy carriers nicotinamide adenine dinucleotide phosphate (reduced form) (NADPH) and adenosine triphosphate (ATP), in the light-independent reactions these energy carriers are then used to fix carbon dioxide via the enzyme ribulose-1,5-bisphosphate carboxylase/ oxygenase (Rubisco) into C3 sugars and regenerate the Rubisco substrate ribulose-1,5-bisphosphate (RuBP; Calvin-Benson-Bassham cycle). Both Rubisco activity and the rates of regeneration reactions have been targeted for improvement, which have proven very successful in recent years (Lefebvre et al, 2005;Kurek et al, 2007;Kumar et al, 2009;Rosenthal et al, 2011;Parry et al, 2013;Whitney et al, 2015;Driever et al, 2017;Salesse-Smith et al, 2018;Simkin et al, 2015Simkin et al, , 2017aSimkin et al, , 2019Scafaro et al, 2019a;López-Calcagno et al, 2020;Iñiguez et al, 2021), with more promising research under way (Scafaro et al, 2019b;Degen et al, 2020).…”

Molecular mechanism of Rubisco activase: Dynamic assembly and Rubisco remodeling

“…Due to the dramatic climate changes, we have an urgent need to either increase crop production or improve the efficiency of carbon fixation to accommodate lowering atmospheric CO 2 . Engineering Rubisco's active site to improve its carboxylation efficiency is one direction to improve photosynthesis (Iñiguez et al, 2021). The temperature-sensitive property of the Rca can also be considered in engineering a crop to adapt to climate change.…”

Singular adaptations in the carbon assimilation mechanism of the polyextremophile cyanobacterium Chroococcidiopsis thermalis

“…Increasing crop yield is a must to face the food needs of the rising population (Ray et al 2013 ) since the decreased arable land and climate change impact on crops represent important risks for plant production (Long et al 2015 ). Bioengineering approaches for photosynthesis optimization have largely demonstrated the potential for enhancing crop yield, for example by enhancing Rubisco carboxylation capacity (reviewed by Iñiguez et al ( 2021 )). Several attempts have tried to enhance photosynthetic rates from crops by introducing some basic CCM components and Rubisco from Cyanobacteria.…”