Hypoxic and Fe‐Responses are Regulated by the ERFVII Factors and the PCO Branch of the N‐Degron Pathway According to Iron Availability

In plants, iron homeostasis and oxygen metabolism are strictly related, indeed several Fe-requiring enzymes catalyze reactions that also involve O₂ as a reagent, product, entry or end point of the pathway. Oxygen sensing itself relies on the Fe-dependent enzymes Plant cysteine oxidases. However, the impact of iron deficiencies on the response to hypoxic stresses has not been investigated so far. PCOs channel the ERFVII ethylene-responsive factors into a proteasomal N-degron pathway that connects hypoxia-inducible responses to the stabilization of the ERFVII transcription factors, which act as master regulators of plant hypoxic transcription. Here, we investigated the interplay between low oxygen and Fe-deficiency stresses in A. thaliana. PCO activity in vivo was inferred from the expression of hypoxia marker genes and from the activity of a genetically encoded reporter of ERFVII protein stability. Our results highlight that Fe deprivation can elicit hypoxia-like responses depending on its severity. Moreover, evidence from the pentuple erfVII mutant indicate that the ERFVIIs take part to the responses to chronic Fe-deficiency and fine-tune nutrient content to the shoot 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.