A phosphoinositide-mediated switch of GET pathway receptor dimerization in Arabidopsis.

The Guided Entry of Tail-Anchored Proteins (GET) pathway facilitates the insertion of tail-anchored (TA) proteins into the ER membrane, but its regulation in plants remains unclear. In Arabidopsis, we identify phosphatidylinositol 4-phosphate (PI4P) as an anchor that brings the receptors AtGET1 and AtGET2 into proximity within the ER membrane. AtGET2 binds PI4P via an arginine residue in its transmembrane domain. Mutation of this residue disrupts AtGET1 and AtGET2 proximity at the ER, impairing GET complex function. This defect can be rescued by synthetic dimerization of AtGET1 and AtGET2. The PI4P phosphatase RHD4 acts as a gatekeeper, converting PI4P to PI and enabling AtGET1-AtGET2 interaction, which influences TA protein insertion and root hair growth. Our findings establish the PI4P-RHD4 module as a crucial regulator of GET receptor dynamics, highlighting the interplay between phospholipids and protein trafficking in plants.