C₂ photosynthesis: a promising route towards crop improvement?

Abstract

C 2 photosynthesis is a carbon concentrating mechanism that can increase net CO 2 assimilation by capturing, concentrating and re-assimilating CO 2 released by photorespiration. Empirical and modelling studies indicate that C 2 plants assimilate more carbon than C 3 plants under high temperature, bright light, and low CO 2 conditions. I argue that engineering C 2 photosynthesis into C 3 crops is a promising approach to improve photosynthetic performance under theseand temporally heterogeneousenvironments, and review the modifications that may recreate a C 2 phenotype in C 3 plants. Although a C 2 engineering program would encounter many of the same challenges faced by C 4 engineering programmes, the simpler leaf anatomical requirements make C 2 engineering a feasible approach to improve crops in the medium term. 1 Table modified from Lundgren & Christin (2017); Voznesenskaya et al. (2017). 2 Lineages in bold lack close C 4 relatives. 3 Diplotaxis muralis is hybrid between D. tenuifolia (C 2) and D. viminea (C 3) (Ueno et al., 2006). 4 Portulaca cryptopetala contains facultative CAM, and this lineage lacks close C 3 relatives.

The effect of increasing temperature on crop photosynthesis: from enzymes to ecosystems

“…Engineering C 2 photosynthesis, a simple CCM that captures, concentrates, and re-assimilates photorespired CO 2 , is a promising approach currently in its infancy. An advantage of C 2 photosynthesis is the ability to exploit native genes and alter only their regulation and expression, as all required genes are present in C 3 species ( Lundgren, 2020 ). Finally, direct manipulations of the photorespiratory pathway can lower the cost of photorespiration.…”

Ensuring Nutritious Food Under Elevated CO2 Conditions: A Case for Improved C4 Crops

“…The main argument made in favor of this approach is that C 2 photosynthesis is a stable intermediate physiological state between C 3 and C 4 metabolism that increases net carbon assimilation under high temperatures (Monson, 1989;Bellasio and Farquhar, 2019). But, importantly, C 2 photosynthesis does not require the complex anatomical changes associated with C 4 photosynthesis (Lundgren, 2020). This strategy could be useful in improving crop yields (or in mitigating yield declines) in the medium term.…”

“…Recently, Lundgren (2020) presented a compelling case for engineering C 2 photosynthesis into C 3 crop plants to improve photosynthetic performance in the face of climate change. The main argument made in favor of this approach is that C 2 photosynthesis is a stable intermediate physiological state between C 3 and C 4 metabolism that increases net carbon assimilation under high temperatures ( Monson, 1989 ; Bellasio and Farquhar, 2019 ).…”

Upregulation of chloroplastic pyruvate dehydrogenase genes in rice leaf would potentially drive the in planta photorespiratory bypass for higher biomass

“…Whether the upregulated plPdc driverts the photorespiratory process or viceversa, is unknown yet. Plants accomplishing C 2 photosynthesis have evolved for the preferential downregulation of mGDC (glycine decarboxylase, mitochondrial) or anatomical rearrangements (with more chloroplasts at the periphery) in mesophyll cells either reduce CO 2 release or provides high resistance to CO 2 e ux 7,24 . This is commonly called 'C 2 shuttle' and helps increase the plant productivity with high biomass or yield.…”