Abstract:

Iron (Fe) is indispensable for the growth and development of plants. It is well known that FER‐LIKE FE DEFICIENCY‐INDUCED TRANSCRIPTION FACTOR (FIT) is a key regulator of Fe uptake in Arabidopsis. Here, we identify the Oryza sativa FIT (also known as OsbHLH156) as the interacting partner of IRON‐RELATED BHLH TRANSCRIPTION FACTOR 2 (OsIRO2) that is critical for regulating Fe uptake. The OsIRO2 protein is localized in the cytoplasm and nucleus, but OsFIT facilitates the accumulation of OsIRO2 in the nucleus. Loss‐of‐function mutations of OsFIT result in decreased Fe accumulation, severe Fe‐deficiency symptoms, and disrupted expression of Fe‐uptake genes. In contrast, OsFIT overexpression promotes Fe accumulation and the expression of Fe‐uptake genes. Genetic analyses indicate that OsFIT and OsIRO2 function in the same genetic node. Further analyses suggest that OsFIT and OsIRO2 form a functional transcription activation complex to initiate the expression of Fe‐uptake genes. Our findings provide a mechanism understanding of how rice maintains Fe homeostasis.