Mediator subunit 16 functions in the regulation of iron uptake gene expression in Arabidopsis

Authors

  • Yue Zhang,

    1. The State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Chaoyang District, Beijing, China
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    • These authors contributed equally to this work.
  • Huilan Wu,

    1. The State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Chaoyang District, Beijing, China
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    • These authors contributed equally to this work.
  • Ning Wang,

    1. The State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Chaoyang District, Beijing, China
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  • Huajie Fan,

    1. The State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Chaoyang District, Beijing, China
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  • Chunlin Chen,

    1. The State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Chaoyang District, Beijing, China
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  • Yan Cui,

    1. The State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Chaoyang District, Beijing, China
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  • Hongfei Liu,

    1. The State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Chaoyang District, Beijing, China
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  • Hong-Qing Ling

    Corresponding author
    1. The State Key Laboratory of Plant Cell and Chromosome Engineering, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Chaoyang District, Beijing, China
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Summary

  • Iron is an essential nutrient for plant growth and development, and its absorption is tightly controlled. Under iron limitation, FIT dimerizes with the four Ib bHLH proteins and activates the expression of iron uptake genes. However, how the dimerized complex activates downstream genes remains unclear.
  • Using forward genetics, a low-iron-sensitive mutant was screened. The corresponding gene (MED16) was isolated, and its biological functions in iron homeostasis were characterized using approaches such as gene expression, protein subcellular localization, protein–protein interaction and chromatin immunoprecipitation assay.
  • Lesion of MED16 significantly reduced FRO2 and IRT1 expression in Arabidopsis roots. The MED16 mutants showed a low shoot iron concentration and severe leaf chlorosis under iron limitation, whereas it grew normally as wild-type under iron sufficiency. Furthermore, we showed that MED16 interacted with FIT and improved the binding of the FIT/Ib bHLH complex to FRO2 and IRT1 promoters under iron-deficient conditions. Additionally, we found that many iron-deficient response genes, which are regulated by FIT, were also controlled by MED16.
  • In conclusion, MED16 is involved in the iron deficiency response, and modulates the iron uptake gene expression under iron limitation. Our results increase the understanding of the molecular regulation mechanisms underlying iron uptake and homeostasis in plants.

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