ERF73/HRE1 is involved in HO production via hypoxia-inducible Rboh gene expression in hypoxia signaling.

Hypoxia deprives cells of energy and induces severe physical damage in embryophytes. Under hypoxia, the equilibrium between ethylene and HO affects the response of the transcription factor AtERF73/HRE1. To evaluate the role of AtERF73/HRE1 during hypoxia signaling, we used three independent AtERF73/HRE1 knockout lines to detect HO accumulation. The results revealed that under hypoxia, HO accumulation in the AtERF73/HRE1 knockout lines decreased, indicating that AtERF73/HRE1 uses a negative feedback regulation mechanism to influence the production of HO induced through hypoxia signal transduction. Quantitative RT-PCR analyses showed that oxygen deficiency had different effects on the expression of the hypoxia-induced genes Rboh B, D, G, and I in the AtERF73/HRE1 knockout lines. In particular, Rboh B and D expression were increased, whereas Rboh G expression was decreased. The expression of Rboh I was increased at 1 h but decreased at 3 h during hypoxia treatment in the AtERF73/HRE1 knockout lines. Similarly, the transcript levels of antioxidant and hypoxia-induced/ethylene response genes in the AtERF73/HRE1 knockout lines were affected by hypoxic stress, indicating that AtERF73/HRE1 is essential to hypoxia signal transduction in embryophytes. Additionally, in histochemical analysis, AtERF73/HRE1 promoter-induced GUS expression was detected in various plant parts throughout the plant growth process (e.g., leaves, inflorescences, siliques), particularly in the edges of mature leaves and guard cells. Taken together, our results confirm that AtERF73/HRE1 plays a role in HO production by affecting the hypoxia-induced expression of Rboh genes in hypoxia signal transduction.