Severe Fe deficiency promotes hypoxia inducible responses in Arabidopsis thaliana
In plants, Fe homeostasis and O2 metabolism are strictly related, indeed several Fe-requiring enzymes catalyze reactions that also involve oxygen, as a reagent, product, entry or end point of the metabolic pathway in which the enzyme takes part. Oxygen sensing itself relies on Fe-dependent enzymes, the Plant cysteine oxidase (PCO) family of 2-OG independent thiol dioxygenases. PCOs are responsible for the degradation of ERFVII ethylene-responsive factors through a proteasomal N-degron pathway that connects hypoxia-inducible responses to the stabilization of the ERFVII transcription factors. Here, we investigated the interplay between low oxygen and Fe-deficiency stresses in A. thaliana. We used plants expressing a genetically encoded reporter of ERFVII protein stability and measured the expression of anaerobic genes to infer PCO activity in vivo. Our results highlight that Fe deprivation can elicit hypoxia-like responses depending on its severity. To test the involvement the ERFVII factors further, we examined the response of a pentuple erfVII mutant to Fe-deficiency stress, individually or combined with low oxygen. Our data indicate that the ERFVIIs might take part to the acclimation to chronic Fe deficiency by acting as positive regulators of starvation-responsive genes. Moreover, our results suggest that the ERFVIIs fine-tune nutrient mobilization to the shoots of submerged plants growing on moderately Fe-deficient substrates. This work expands the known functions of the ERFVII factors and provides new information to understand plant responses to combined environmental stresses.