MPK3-mediated phosphorylation inactivates MYB4 to promote FIT-dependent iron acquisition.

MPK3 phosphorylation at Serine 4 inactivates MYB4, enabling FIT-dependent iron uptake in Arabidopsis under deficiency conditions.

• Why it matters: Iron homeostasis is vital for plant growth, yet the regulatory mechanisms controlling Fe acquisition are not fully understood, especially the role of negative regulators like MYB4.
• What they did: The study used molecular interaction assays and phosphorylation analysis to show that MPK3 phosphorylates MYB4 at Serine 4, leading to its degradation and relieving repression of Fe-uptake genes.
• The result: This phosphorylation-dependent inactivation of MYB4 promotes FIT dimerization with bHLH partners, activating Fe uptake genes and revealing a new regulatory module for Fe homeostasis.