Degradation of <scp>PbrDGK4</scp> impairs pollen tube endocytosis in pear self‐incompatibility by reducing <scp>PbrAP1</scp> /2β phosphorylation

Pear (Pyrus bretschneideri) self-incompatibility (SI) is an S-RNase-based system that arrests incompatible pollen tube growth, but the molecular mechanism by which SI regulates endocytosis (a key process for pollen tube polarity) remains unclear. Live-cell imaging, Phos-tag immunoblots, molecular docking, gene silencing, mutant complementation, and ubiquitination assays were combined to dissect the regulatory pathway. Incompatible S-RNase impairs clathrin-mediated endocytosis (CME). The AP-1/AP-2 shared β-subunit PbrAP1/2β is essential for CME, with Ser228 phosphorylation enhancing AP-2 complex stability. Pollen tube-specific kinase PbrDGK4 maintains PbrAP1/2β phosphorylation via interaction. SI-induced E3 ligase PbrARI2.3 mediates K48-linked ubiquitination (K60/K254) and degradation of PbrDGK4, reducing PbrAP1/2β phosphorylation. S-RNase triggers PbrDGK4 degradation, lowering PbrAP1/2β Ser228 phosphorylation and impairing CME, ultimately arresting incompatible pollen tube growth, advancing insights into SI-regulated pollen tube polarity.