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.