Phospho-mutant activity assays provide evidence for alternative phospho-regulation pathways of the transcription factor FER-LIKE IRON DEFICIENCY-INDUCED TRANSCRIPTION FACTOR

Regina Gratz, Tzvetina Brumbarova, Rumen Ivanov, Ksenia Trofimov, Laura Tünnermann, Rocio Ochoa-Fernandez, Tim Blomeier, Johannes Meiser, Stefanie Weidtkamp-Peters, Matias D. Zurbriggen, Petra Bauer*

*Corresponding author for this work

Research output: Contribution to journalArticleResearchpeer-review

18 Citations (Scopus)

Abstract

The key basic helix–loop–helix (bHLH) transcription factor in iron (Fe) uptake, FER-LIKE IRON DEFICIENCY-INDUCED TRANSCRIPTION FACTOR (FIT), is controlled by multiple signaling pathways, important to adjust Fe acquisition to growth and environmental constraints. FIT protein exists in active and inactive protein pools, and phosphorylation of serine Ser272 in the C-terminus, a regulatory domain of FIT, provides a trigger for FIT activation. Here, we use phospho-mutant activity assays and study phospho-mimicking and phospho-dead mutations of three additional predicted phosphorylation sites, namely at Ser221 and at tyrosines Tyr238 and Tyr278, besides Ser 272. Phospho-mutations at these sites affect FIT activities in yeast, plant, and mammalian cells. The diverse array of cellular phenotypes is seen at the level of cellular localization, nuclear mobility, homodimerization, and dimerization with the FIT-activating partner bHLH039, promoter transactivation, and protein stability. Phospho-mimicking Tyr mutations of FIT disturb fit mutant plant complementation. Taken together, we provide evidence that FIT is activated through Ser and deactivated through Tyr site phosphorylation. We therefore propose that FIT activity is regulated by alternative phosphorylation pathways.

Original languageEnglish
Pages (from-to)250-267
Number of pages18
JournalNew Phytologist
Volume225
Issue number1
DOIs
Publication statusPublished - 1 Jan 2020

Keywords

  • Arabidopsis
  • FIT
  • IRT1
  • bHLH039
  • iron uptake
  • serine phosphorylation
  • transcription factor
  • tyrosine phosphorylation

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