Iron (Fe) is a vital micronutrient for plants, which is required for processes such as photosynthesis and enzyme activity. Plants must carefully manage iron levels to maintain health and productivity. They activate iron uptake genes when deficient and suppress them when iron is excessive to prevent toxicity. This careful balance is known as iron homeostasis.

Two main strategies have been identified which plants use to acquire iron: a reduction-based method and a chelation-based method. Root responses to iron shortage have been widely studied, but much less is known about how shoots, which make up most of a plant’s biomass and require more iron, regulate their iron status.

In a study published in The Plant Cell, researchers from the Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences revealed how a network of proteins works together to regulate iron balance throughout the whole plant, which fills the gap in understanding how plants manage this essential nutrient.

Researchers investigated the role of iron sensors BRUTUS (BTS) and its related proteins BTS-LIKE1/2 (BTSL1/2), along with a group of transcription factors called bHLH IVc in regulating iron homeostasis. Using Arabidopsis thaliana as a model, they identified central regulatory proteins that direct distinct iron-deficiency responses in roots and shoots.

It was found that BTS safeguarded plant health by preventing iron overaccumulation in shoots and mitigating iron toxicity, while BTSL1/2, predominantly active in roots, functioned to downregulate iron-deficiency responses and control iron uptake. Besides, bHLH IVc transcription factors were showed to interact with BTSL1/2 to mediate iron balance between roots and aerial tissues.

Experimental data showed that the bts-2 mutant displayed leaf chlorosis and sterility phenotypes under iron-sufficient conditions, along with significant upregulation of reactive oxygen species (ROS)-related genes, which highlights the critical function of BTS in preventing iron overload toxicity.

“Our study helps solve the long-standing question of how iron signaling is coordinated across the whole plant. It reveals a functional division of labor among regulatory proteins, and identifies the bHLH IVc group as a central hub for systemic iron homeostasis,” said LIANG Gang from XTBG, the corresponding author of this study.

Growth of Arabidopsis thaliana under different treatments. (Image by ZHAO Junhui)