HSP90 differentially stabilizes plant ABCB-type auxin transporters on the plasma membrane

Closely related FKBP orthologs, FKBP42/TWISTED DWARF1 (TWD1) and FKBP38, have been shown to control the biogenesis of plant and mammalian ATP-binding cassette (ABC) transporters, respectively. However, the mechanistic role of the described FKBP-ABCB interaction is widely unknown. Here, we verify cytosolic HEAT-SHOCK PROTEIN90 (HSP90) isoforms as valid interactors of TWD1 and map HSP90 binding to an amphiphilic alpha-helix preceding its TPR domain. We provide pharmacological and genetic evidence that a subset of TWD1-interacting ABCBs, in contrast to mammalian ABCBs, are constitutive HSP90 clients in plants. This effect and its specificity are presumably provided by TWD1. Our data strongly correlate the impact of HSP90 inhibition on ABCB-mediated development and ABCB plasma membrane stability on the one hand and ABCB cycling rate on the other. In summary, we uncover a dynamic mechanism of HSP90 for differential stabilization of the plasma membrane ABCB isoforms to regulate polar auxin transport and to confer developmental plasticity.