The researchers first tested whether the expression of IMA genes is responsive to changes in Cu concentration and found that the transcription of IMA genes is repressed by Cu deficiency. Combined disruption of all IMA genes resulted in increased tolerance to Cu deficiency and increased transcript abundance of Cu uptake genes, whereas the overexpression of IMA1 or IMA3 had the opposite effect.
The researchers then performed protein interaction assay studies and found that IMAs interact with Cu-DEFICIENCY INDUCED TRANSCRIPTION FACTOR1 (CITF1), which is a positive regulator of the Cu uptake genes.
Furthermore, IMAs not only interfere with the DNA binding of CITF1, but also repress the transcriptional activation activity of CITF1, hence resulting in the downregulation of the Cu uptake genes. When Cu is sufficient, IMAs block CITF1 from binding to the promoters of the Cu uptake genes and stop CITF1 from activating the Cu uptake genes. When Cu is deficient, the expression of IMAs is repressed.
The results suggest that IMAs physically interact with CITF1 and negatively regulate the Cu-deficiency response by inhibiting the DNA binding and transcriptional activation.
"This study suggests that IMAs are a new component of the Cu deficiency response signaling pathway. It provides experimental support for the existence of a sophisticated system that allows plants to dynamically respond to Cu status," said LIANG Gang of XTBG.
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