Abstract
Plants depend on the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) for CO2 fixation. However, especially in C3 plants, photosynthetic yield is reduced by formation of 2-phosphoglycolate, a toxic oxygenation product of Rubisco, which needs to be recycled in a high-flux-demanding metabolic process called photorespiration. Canonical photorespiration dissipates energy and causes carbon and nitrogen losses. Reducing photorespiration through carbon-concentrating mechanisms, such as C4 photosynthesis, or bypassing photorespiration through metabolic engineering is expected to improve plant growth and yield. The β-hydroxyaspartate cycle (BHAC) is a recently described microbial pathway that converts glyoxylate, a metabolite of plant photorespiration, into oxaloacetate in a highly efficient carbon-, nitrogen-, and energy-conserving manner. Here, we engineered a functional BHAC in plant peroxisomes to create a photorespiratory bypass that is independent of 3-phosphoglycerate regeneration or decarboxylation of photorespiratory precursors. While efficient oxaloacetate conversion in Arabidopsis thaliana still masks the full potential of the BHAC, nitrogen conservation and accumulation of signature C4 metabolites demonstrate the proof of principle, opening the door to engineering a photorespiration-dependent synthetic carbon-concentrating mechanism in C3 plants.
Highlights
AGAT, BHAD, and iminosuccinate reductase (ISR) were C terminally fused with PTS1 [26]
We further focused on the metabolite profile of BHAC plants in comparison to the wild-type Col-0 (WT) and ggt1-1 mutant backgrounds grown under photorespiratory conditions in ambient air (Fig. 4B)
We report on engineering a functional BHAC in Arabidopsis peroxisomes to demonstrate a photorespiratory bypass independent
Summary
Especially in C3 plants, photosynthetic yield is reduced by formation of 2-phosphoglycolate, a toxic oxygenation product of Rubisco, which needs to be recycled in a high-flux–demanding metabolic process called photorespiration. The β-hydroxyaspartate cycle (BHAC) is a recently described microbial pathway that converts glyoxylate, a metabolite of plant photorespiration, into oxaloacetate in a highly efficient carbon-, nitrogen-, and energy-conserving manner. While efficient oxaloacetate conversion in Arabidopsis thaliana still masks the full potential of the BHAC, nitrogen conservation and accumulation of signature C4 metabolites demonstrate the proof of principle, opening the door to engineering a photorespirationdependent synthetic carbon–concentrating mechanism in C3 plants. Future agriculture must reconcile sustainability with increased productivity to supply global food demands that will have doubled by 2050 [1, 2] To fulfill this goal, agricultural yields will have to increase annually by 2.4%. In high-yielding crop varieties, both plant architecture and the harvest index—the fraction of total energy in plant biomass contained in the harvestable organs—approach their theoretical limits [5]
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