IRON MAN sequesters BTS to activate iron deficiency response (PNAS)

Plants need to maintain an optimum level of iron (Fe) for normal growth and development. Many Fe-responsive molecular players have been identified in Arabidopsis, including the IRON MAN (IMA) peptides. These peptides are induced by Fe deficiency, but their role in maintaining Fe homeostasis remains poorly understood. Li et al. provide a mechanistic insight into the role of IMA in the Fe-uptake pathway. They found that IMAs harbor a BRUTUS (BTS) interaction domain (BID) in their C-terminus which enables them to interact with BTS, a negative regulator of Fe uptake. Further, the bHLH transcription factors 105 and 115 which positively regulate Fe uptake also contain BID. Under Fe-sufficient conditions, the bHLH105/115 proteins undergo ubiquitination and degradation by the action of BTS. However, under Fe deficiency when IMAs are expressed, competitive binding of IMAs with BTS leads to BTS sequestration, protecting bHLH105/115 from degradation and allowing them to positively regulate the Fe-uptake pathway. The findings of this study show that sequestration of BTS by IMA is essential for activating Fe deficiency response in Arabidopsis. (Summary by Chandan Kumar Gautam @chandan_gautam) PNAS 10.1073/pnas.2109063118