Hierarchical regulation of oxygen-sensing through coupled transducers in Arabidopsis thaliana.

The sensing of molecular oxygen is an essential component of development and environmental response in both animals and plants. Few substrates of the plant oxygen-sensing PLANT CYSTEINE OXIDASE (PCO) N-degron pathway have been identified. Here we show that HYPOXIA TRANSDUCER1 (HYT1, previously named HYPOXIA-RESPONSIVE UNKNOWN PROTEIN, HUP40), an angiosperm-specific tail anchored-domain protein, is a substrate of this pathway through a Cys-2 dependent N-degron. HYT1 is stabilised in response to acute hypoxia in root tissues and is associated with the endoplasmic reticulum and nucleus. Genetic evidence shows that HYT1 is an important component in the transduction of oxygen-sensing, required for tolerance to acute hypoxia and other stress responses. Expression of HYT1 is directly activated by group VII ETHYLENE RESPONSE FACTOR transcription factors (ERFVIIs), that are also pathway substrates. The relationship between ERFVIIs and HYT1 has properties of a coherent feed-forward loop initiated and maintained by hypoxia, providing a mechanism to ensure robust response to reduced oxygen.