Self-incompatibility requires GPI anchor remodeling by the poppy PGAP1 orthologue HLD1

Glycosylphosphatidylinositol anchored proteins (GPI-APs) are tethered to the outer leaflet of the plasma membrane where they function as key regulators of a plethora of biological processes in eukaryotes. Self-incompatibility (SI) plays a pivotal role regulating fertilization in higher plants through recognition and rejection of ‘self’ pollen. Here we used Arabidopsis thaliana lines engineered to be self-incompatible by expression of Papaver rhoeas SI determinants for an SI suppressor screen. We identify HLD1/AtPGAP1 , an ortholog of the human GPI-inositol deacylase PGAP1 , as a critical component required for the SI response. Besides a delay in flowering time, no developmental defects were observed in hld1/atpgap1 knockout plants, but SI was completely abolished. We demonstrate that HLD1/AtPGAP1 functions as a GPI-inositol deacylase and that this GPI-remodeling activity is essential for SI. Using GFP–SKU5 as a representative GPI-AP, we show that the HLD1/AtPGAP1 mutation does not affect GPI-AP production and targeting but affects their cleavage and release from membranes in vivo . Our data not only implicate GPI-APs in SI, providing new directions to investigate SI mechanisms, but also identify a key functional role for GPI-AP remodeling by inositol deacylation in planta .