OsbHLH062 regulates iron homeostasis by inhibiting iron deficiency responses in rice.

Iron (Fe) homeostasis in plant cells is crucial for crop productivity and quality. An intricate transcriptional network involving numerous basic Helix-Loop-Helix (bHLH) transcription factors has been proposed to control Fe homeostasis. In the present study, we characterized rice (Oryza sativa) OsbHLH062, a member of the IVb subgroup of the bHLH family, demonstrating that it negatively regulates Fe-deficiency responses. OsbHLH062 represses transcription by recruiting TOPLESS/TOPLESS-RELATED co-repressors (TPL/TPRs) through its ethylene-responsive element binding factor-associated amphiphilic repression (EAR) motif. Under Fe deficiency, the expression of OsbHLH062 is upregulated in roots and downregulated in shoots. Overexpression of OsbHLH062 leads to decreased Fe accumulation in the shoot. Furthermore, OsbHLH062 interacts with POSITIVE REGULATOR OF IRON HOMEOSTASIS 1 (OsPRI1) and inhibits its transactivation activity, thereby negatively regulating the expression of many Fe homeostasis-related genes. These results indicate an important role for OsbHLH062 in regulating Fe homeostasis by negatively regulating Fe deficiency responses in rice. This knowledge will aid in the design of Fe-biofortified rice plants that can help to address the global issue of Fe deficiency.