Oxygen and hypoxia

The majority of eukaryotic organisms rely on molecular oxygen for respiratory energy production. When the supply of oxygen is hampered, a variety of acclimation responses is activated to reduce detrimental effects of energy depletion. Various oxygen sensing mechanisms have been described in the past to trigger these responses, but each of them appears to be kingdom specific and no sensor has been found in plants until now. Here, we show that one branch of the ubiquitin-dependent N-end rule pathway for protein degradation, which is active both in mammals and plants, functions as an oxygen sensing mechanism in plants.

We identified a conserved N-terminal amino acid sequence of the ERF-transcription factor RAP2.12 to be dedicated to an oxygen-dependent sequence of post-translational modifications, which ultimately leads to degradation of RAP2.12 under aerobic conditions. The modification that triggers this pathway is catalyzed by a Plant specific class of Cysteine Oxidases that incorporates molecular oxygen into cysteine to generate a sulfinic-acid adduct. When the oxygen concentration is low, RAP2.12 is released from the plasma membrane and accumulates in the nucleus to activate the gene expression program for hypoxia acclimation. Our discovery of an oxygen sensing mechanism opens up new possibilities to improve flooding tolerance in crops.