A cyanobacterial photorespiratory bypass model to enhance photosynthesis by rerouting photorespiratory pathway in C3 plants

Plants employ photosynthesis to produce sugars for supporting their growth. During photosynthesis, an enzyme Ribulose 1,5 bisphosphate carboxylase/oxygenase (Rubisco) combines its substrate Ribulose 1,5 bisphosphate (RuBP) with CO2 to produce phosphoglycerate (PGA). Alongside, Rubisco also takes up O-2 and produce 2-phosphoglycolate (2-PG), a toxic compound broken down into PGA through photorespiration. Photorespiration is not only a resource-demanding process but also results in CO2 loss which affects photosynthetic efficiency in C-3 plants. Here, we propose to circumvent photorespiration by adopting the cyanobacterial glycolate decarboxylation pathway into C-3 plants. For that, we have integrated the cyanobacterial glycolate decarboxylation pathway into a kinetic model of C-3 photosynthetic pathway to evaluate its impact on photosynthesis and photorespiration. Our results show that the cyanobacterial glycolate decarboxylation bypass model exhibits a 10% increase in net photosynthetic rate (A) in comparison with C-3 model. Moreover, an increased supply of intercellular CO2 (C-i) from the bypass resulted in a 54.8% increase in PGA while reducing photorespiratory intermediates including glycolate (-49%) and serine (-32%). The bypass model, at default conditions, also elucidated a decline in phosphate-based metabolites including RuBP (-61.3%). The C-3 model at elevated level of inorganic phosphate (Pi), exhibited a significant change in RuBP (+355%) and PGA (-98%) which is attributable to the low availability of C-i. Whereas, at elevated Pi, the bypass model exhibited an increase of 73.1% and 33.9% in PGA and RuBP, respectively. Therefore, we deduce a synergistic effect of elevation in CO2 and Pi pool on photosynthesis. We also evaluated the integrative action of CO2, Pi, and Rubisco carboxylation activity (V-cmax) on A and observed that their simultaneous increase raised A by 26%, in the bypass model. Taken together, the study potentiates engineering of cyanobacterial decarboxylation pathway in C-3 plants to bypass photorespiration thereby increasing the overall efficiency of photosynthesis.