Phase Separation of a Nodulin Sec14-like protein Maintains Auxin Efflux Carrier Polarity at Arabidopsis Plasma Membranes

Robust development can be modulated by local protein accumulation which is sometimes manifested as polarity patterns; yet, the mechanisms that lead to these patterns are largely unknown. Using the model plant Arabidopsis, we report that auxin-induced polar patterns can be reinforced by the phase transition of a SEC14-like lipid-binding protein at the plasma membrane. Using imaging, genetics, and in vitro reconstitutions, we show that the SEC14-like phase transition is promoted outside the stem cell root niche through its association with the caspase-like protease separase and conserved microtubule motors in a plasma membrane interface. Separase cleaves SEC14-like to promote its transition from liquid-like clusters to solid-like filaments. Filaments self-amplify and potentiate the robustness and maintenance of plasma membrane domains through associations with polar proteins. This work uncovers that robust cell patterns involve proteolysis-mediated phase transitions at unpreceded plasma membrane interfaces. ### Competing Interest Statement The authors have declared no competing interest.