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Proteasome‐mediated turnover of the transcriptional activator FIT is required for plant iron‐deficiency responses
Author(s) -
Sivitz Alicia,
Grinvalds Claudia,
Barberon Marie,
Curie Catherine,
Vert Grégory
Publication year - 2011
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/j.1365-313x.2011.04565.x
Subject(s) - arabidopsis , proteasome , iron deficiency , transcription factor , microbiology and biotechnology , transcriptional regulation , ferrous , arabidopsis thaliana , biology , ubiquitin ligase , chemistry , biochemistry , ubiquitin , gene , mutant , medicine , organic chemistry , anemia
Summary Plants display a number of responses to low iron availability in order to increase iron uptake from the soil. In the model plant Arabidopsis thaliana , the ferric‐chelate reductase FRO2 and the ferrous iron transporter IRT1 control iron entry from the soil into the root epidermis. To maintain iron homeostasis, the expression of FRO2 and IRT1 is tightly controlled by iron deficiency at the transcriptional level. The basic helix–loop–helix (bHLH) transcription factor FIT represents the most upstream actor known in the iron‐deficiency signaling pathway, and directly regulates the expression of the root iron uptake machinery genes FRO2 and IRT1 . However, how FIT is controlled by iron and acts to activate transcription of its targets remains obscure. Here we show that FIT mRNA and endogenous FIT protein accumulate in Arabidopsis roots upon iron deficiency. However, using plants constitutively expressing FIT , we observed that FIT protein accumulation is reduced in iron‐limited conditions. This post‐transcriptional regulation of FIT is perfectly synchronized with the accumulation of endogenous FIT and IRT1 proteins, and therefore is part of the early responses to low iron. We demonstrated that such regulation affects FIT protein stability under iron deficiency as a result of 26S proteasome‐dependent degradation. In addition, we showed that FIT post‐translational regulation by iron is required for FRO2 and IRT1 gene expression. Taken together our results indicate that FIT transcriptional and post‐translational regulations are integrated in plant roots to ensure that the positive regulator FIT accumulates as a short‐lived protein following iron shortage, and to allow proper iron‐deficiency responses.