IRONMAN interacts with OsHRZ1 and OsHRZ2 to maintain Fe homeostasis.

IRONMAN (IMA) is a family of small peptides which positively regulate the Fe deficiency response. However, the molecular mechanism by which OsIMA1 and OsIMA2 regulate Fe homeostasis was unclear. Here, we reveal that OsIMA1 and OsIMA2 interact with the potential Fe sensors, OsHRZ1 and OsHRZ2. OsIMA1 and OsIMA2 contain a conserved 17-amino acid C-terminal region which is responsible for the interactions with OsHRZ1 and OsHRZ2. The OsIMA1ox plants have increased seed Fe concentration and reduced fertility, as observed in the hrz1-2 loss-of-function mutant plants. Moreover, the expression trends of Fe deficiency inducible genes in the OsIMA1ox plants are the same as those in the hrz1-2. Co-expression assays suggest that OsHRZ1 and OsHRZ2 promote the degradation of OsIMA1 proteins. As the interaction partners of OsHRZ1, the OsPRI proteins also interact with OsHRZ2. The conserved C-terminal region of four OsPRIs contributes to the interactions with OsHRZ1 and OsHRZ2. An artificial IMA (aIMA) derived from the C-terminal of OsPRI1 can be also degraded by OsHRZ1. Moreover, the aIMAox rice plants accumulate more Fe without reduction of fertility. This work establishes the link between OsIMAs and OsHRZs, and develops a new strategy for Fe fortification in rice.