PLOS Biology · 19 authors, 11 centres
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Using imaging, genetics, and in vitro reconstitution in Arabidopsis, this study shows that the plasma membrane lipid-binding protein SFH8 undergoes liquid-to-solid phase transitions driven by separase proteolysis at polar plasma membrane interfaces. The solidified, processed form of SFH8—not the liquid form—interacts with and regulates PIN2 polarity, contributing to robust root development.
This preclinical study in Arabidopsis used imaging, genetics, and in vitro reconstitution to investigate phase transitions of the SEC14-like protein SFH8 at plasma membranes. SFH8 forms liquid-like phase-separated condensates at the root stem cell niche. Outside this niche, SFH8 associates with the caspase-like protease separase (ESP) and conserved microtubule motors at unique polar plasma membrane interfaces, where separase cleaves SFH8, promoting its liquid-to-solid transition. Lines expressing an uncleavable SFH8 variant or mutants of separase and associated microtubule motors showed similar developmental phenotypes, indicating the transition is functionally important. The processed and solidified form, but not the liquid form, interacts with and regulates polarity of the auxin efflux carrier PINFORMED2. The work establishes an example of LLPS with importance for plasma membrane micropatterning.
