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MPK3-mediated phosphorylation inactivates MYB4 to promote FIT-dependent iron acquisition
Hui Song1, Guangna Chen1, Jiena Xu1
1School of Food and Biological Engineering, Hefei University of Technology, Hefei, China.
Abstract:
Iron (Fe) is an essential micronutrient for plant growth, and its homeostasis is critically regulated by the transcription factor FIT in response to deficiency. Here, we identify the R2R3-MYB transcription factor MYB4 as a previously unknown negative regulator of Fe acquisition. MYB4 directly interacts with FIT, competing with bHLH38/39 to prevent the formation of transcriptionally active heterodimers, thereby repressing the expression of the key Fe-uptake genes IRT1 and FRO2. We establish that the mitogen-activated protein kinase MPK3 acts upstream in this pathway. Under Fe-deficient conditions, MPK3 is activated and directly phosphorylates MYB4 at Serine 4, promoting its proteasome-dependent destabilization. This post-translational switch releases FIT to dimerize with bHLH partners, activating Fe uptake. Our work unveils the MPK3-MYB4-FIT signaling module as a previously unrecognized regulatory module that contributes to the dynamic control of Fe homeostasis in Arabidopsis.
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