Figure 10.

Model for the regulation of Fe uptake and homeostasis by MdBT2 by posttranslational modulation of the MdbHLH104 protein. High levels of iron result in the increased accumulation of the MdBTs. The stabilized MdBT proteins interact with MdCUL3s to form an active E3 ligase complex and catalyze the ubiquitination modification and the subsequent degradation of MdbHLH104 proteins via the 26S proteasome pathway. Finally, MdBTs regulate the expression of downstream target genes, such as MdAHA8, and modulate Fe absorption and homeostasis. Under low iron conditions, MdBTs are destabilized, resulting in the accumulation of MdbHLH104 protein to high levels, which promotes Fe uptake.