Iron (Fe) is essential for plant growth and plays critical roles in photosynthesis, respiration, and metabolism. However, the availability of iron in soil varies greatly. Too little iron impairs growth and metabolism, while excessive accumulation can be toxic.

In a study published in The Plant Cell on June 13, researchers from the Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences have identified a protein called COPPER DEFICIENCY INDUCED TRANSCRIPTION FACTOR 1 (CITF1) that negatively regulates iron uptake in Arabidopsis thaliana. They found that CITF1 controls iron uptake by directly interacting with FER-LIKE IRON DEFICIENCY-INDUCED TRANSCRIPTION FACTOR (FIT), a master regulator that activates genes responsible for iron absorption.

To unravel this regulatory mechanism, the researchers employed a multi-faceted approach, combining phenotypic analysis, genetic validation, protein interaction assays, subcellular localization studies, and biochemical functional analyses.

Their experiments showed that under low-iron conditions, citf1 mutant plants developed longer roots, enhanced rhizosphere acidification, and increased iron reductase activity. Conversely, plants overexpressing CITF1 showed reduced iron absorption. Crucially, deleting the FIT gene eliminated the effect of CITF1 on iron nutrition, proving that CITF1's regulation of iron uptake depends entirely on FIT.

Further investigation revealed that CITF1 does not merely activate or deactivate FIT; rather, it fine-tunes FIT activity through three distinct pathways: interfering with the interaction between BTSL1/2 and FIT, relocating FIT protein from the nucleus to the cytoplasm, and forming a FIT–CITF1 dimer that suppresses FIT-mediated activation of iron-uptake genes. These layered controls enable plants to adjust their iron absorption dynamically in response to fluctuating environmental iron levels.

The findings carry significant practical implications. Iron deficiency is a leading cause of crop yield losses and a major contributor to human malnutrition, particularly iron-deficiency anemia. By manipulating regulators such as CITF1, it may become possible in the future to engineer crops that absorb optimal amounts of iron, even under challenging soil conditions.

"Our work reveals a novel post-translational regulatory layer in iron homeostasis. CITF1 acts as a molecular rheostat, not an on-off switch, allowing plants to adapt their iron uptake to environmental cues," said LIANG Gang of XTBG.