CIPK11-Dependent Phosphorylation Modulates FIT Activity to Promote Arabidopsis Iron Acquisition in Response to Calcium Signaling

Regina Gratz, Prabha Manishankar, Rumen Ivanov, Philipp Köster, Inga Mohr, Ksenia Trofimov, Leonie Steinhorst, Johannes Meiser, Hans Jörg Mai, Maria Drerup, Sibylle Arendt, Michael Holtkamp, Uwe Karst, Jörg Kudla, Petra Bauer*, Tzvetina Brumbarova

*Corresponding author for this work

Research output: Contribution to journalArticleResearchpeer-review

76 Citations (Scopus)


Nutrient acquisition is entangled with growth and stress in sessile organisms. The bHLH transcription factor FIT is a key regulator of Arabidopsis iron (Fe) acquisition and post-translationally activated upon low Fe. We identified CBL-INTERACTING PROTEIN KINASE CIPK11 as a FIT interactor. Cytosolic Ca 2+ concentration and CIPK11 expression are induced by Fe deficiency. cipk11 mutant plants display compromised root Fe mobilization and seed Fe content. Fe uptake is dependent on CBL1/CBL9. CIPK11 phosphorylates FIT at Ser272, and mutation of this target site modulates FIT nuclear accumulation, homo-dimerization, interaction with bHLH039, and transcriptional activity and affects the plant's Fe-uptake ability. We propose that Ca 2+ -triggered CBL1/9-mediated activation of CIPK11 and subsequent phosphorylation of FIT shifts inactive into active FIT, allowing regulatory protein interactions in the nucleus. This biochemical link between Fe deficiency and the cellular Ca 2+ decoding machinery represents an environment-sensing mechanism to adjust nutrient uptake.

Original languageEnglish
Pages (from-to)726-740.e10
JournalDevelopmental Cell
Issue number5
Publication statusPublished - 11 Mar 2019
Externally publishedYes


  • CBL
  • CIPK11
  • FIT
  • bHLH039
  • iron deficiency
  • nucleocytoplasmic partitioning
  • protein interaction
  • protein mobility
  • protein phosphorylation
  • stress


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