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Phospho‐mutant activity assays provide evidence for alternative phospho‐regulation pathways of the transcription factor FER‐LIKE IRON DEFICIENCY‐INDUCED TRANSCRIPTION FACTOR
Author(s) -
Gratz Regina,
Brumbarova Tzvetina,
Ivanov Rumen,
Trofimov Ksenia,
Tünnermann Laura,
OchoaFernandez Rocio,
Blomeier Tim,
Meiser Johannes,
WeidtkampPeters Stefanie,
Zurbriggen Matias D.,
Bauer Petra
Publication year - 2020
Publication title -
new phytologist
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.742
H-Index - 244
eISSN - 1469-8137
pISSN - 0028-646X
DOI - 10.1111/nph.16168
Subject(s) - transactivation , transcription factor , phosphorylation , mutant , complementation , basic helix loop helix , biology , microbiology and biotechnology , signal transduction , serine , transcription (linguistics) , protein fragment complementation assay , biochemistry , chemistry , dna binding protein , gene , linguistics , philosophy
Summary 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 bHLH 039, 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.