Oxygen Sensing in Plants.

Hypoxia in plants is detrimental to plant growth and crop productivity. It typically arises from adverse environmental conditions that limit oxygen availability, thereby restricting mitochondrial respiration. However, hypoxia also occurs in specific plant tissues where oxygen levels are low due to intense respiratory activity or limited oxygen diffusion. Under these conditions, the existence of a molecular oxygen-sensing mechanism directs plant metabolism and developmental pathways, matching plant fitness to the environment. Oxygen sensing also allows hypoxia to act as a developmental cue, guiding cells toward their appropriate fate. Here, we describe the oxygen-sensing mechanism in plants. Oxygen is used by a class of enzymes known as plant cysteine oxidases (PCOs), which act on specific protein substrates by oxidizing their amino-terminal cysteine residue, thereby targeting them for degradation. This process makes the stability of these proteins dependent on the absence of oxygen and triggers a cascade of molecular events that regulate plant growth and development.