Shortcutting photorespiration: avenues and challenges toward realizing higher-yielding photorespiratory bypass crops.

Photorespiration is a major source of photosynthetic inefficiency in C3 crops. In photorespiration, the oxygenation rather than carboxylation of RuBP by Rubisco triggers an energy-expensive pathway to recycle inhibitory byproducts and recapture lost carbon, ultimately reducing yields. Shortcutting the native pathway through the introduction of photorespiratory bypasses offers a potential route to increase crop yields. In the last decade, several shortcut pathways have been extended from in vitro and controlled environment proof-of-concept experiments to demonstrated yield increases in replicated field trials. This review summarizes current published bypasses and field trial results, discussing potential and challenges for these alternative pathways to be translated into crop species as a tool for improved food security, and to future-proof crops for forecast climate change scenarios. Required focus areas to advance theory to reality include a greater understanding of bypass energetics; increased knowledge of the behavior of photorespiratory bypass metabolomic fluxes; exposure of the mechanisms underpinning the thermotolerant properties of some alternative pathways; and the need for collaborative breeder-style trials in multi-environment locations to confirm and understand the drivers of photorespiratory bypass crop yield increases at various crop growth stages.