The transcription factor Dof3.6/OBP3 regulates iron homeostasis in Arabidopsis

Iron is an essential element for plants. Iron uptake by plants is highly regulated, but the underlying mechanism is poorly understood. Using a truncated fragment of the iron deficiency-responsive bHLH100 gene promoter, we screened the Arabidopsis transcription factor yeast one-hybrid (Y1H) library and identified the DOF family protein, OBP3, as a crucial component of the iron deficiency-signaling pathway. OBP3 is a transcriptional repressor with a C-terminal activation domain. Its expression is induced by iron deficiency. The transgenic lines that overexpress OBP3 exhibited iron overload and premature leaf necrosis, while the obp3 mutant was less tolerant of iron deficiency. It was discovered that OBP3 directly targets the Ib subgroup of bHLH gene promoters. OBP3 interacts with the bHLH transcription factor ILR3 (IAA-LEUCINE RESISTANT3), and their interaction enhances the DNA-binding ability and transcriptional promoting activity of OBP3, resulting in the positive regulation of iron deficiency-response genes. In addition, the E3 Ligase BRUTUS facilitates 26S proteasome-mediated degradation of OBP3 protein to prevent excessive iron uptake in plants. In conclusion, our research emphasizes the vital role of OBP3 in regulating plant iron homeostasis.