Analysis of Plant-Specific ANTH Domain–Containing Protein in Marchantia polymorpha.

This article focuses on the identification and characterization of a novel adaptor protein, phosphatidylinositol-binding clathrin assembly protein-K (PICALM-K), in the liverwort Marchantia polymorpha, which contains both an AP180 N-terminal homology (ANTH) domain and a kinase domain. PICALM-K is distinct from canonical ANTH proteins involved in clathrin-mediated endocytosis, showing specific expression in male reproductive organs and localization at the base of flagella in spermatids, suggesting a flagella-related function. Phylogenetic analysis indicates that PICALM-K originated early in green plant evolution through exon shuffling and was subsequently lost in multiple lineages, correlating with the presence of motile flagella. Although mutants lacking MpPICALM-K show no obvious defects in sperm morphology or motility by conventional observation, deep learning–based video classification revealed subtle differences in spermatozoid movement, supporting a specialized role for PICALM-K in flagellar function distinct from canonical ANTH proteins.