The Endocytosis of Cellulose Synthase in Arabidopsis Is Dependent on m2, a Clathrin-Mediated Endocytosis Adaptin1[W][OPEN]

Clathrin-mediated endocytosis (CME) is the best-characterized type of endocytosis in eukaryotic cells. Plants appear to possess all of the molecular components necessary to carry out CME; however, functional characterization of the components is still in its infancy. A yeast two-hybrid screen identified m2 as a putative interaction partner of CELLULOSE SYNTHASE6 (CESA6). Arabidopsis (Arabidopsis thaliana) m2 is homologous to the medium subunit 2 of the mammalian ADAPTOR PROTEIN COMPLEX2 (AP2). In mammals, the AP2 complex acts as the central hub of CME by docking to the plasma membrane while concomitantly recruiting cargo proteins, clathrin triskelia, and accessory proteins to the sites of endocytosis. We confirmed that m2 interacts with multiple CESA proteins through the m-homology domain of m2, which is involved in specific interactions with endocytic cargo proteins inmammals. Consistent with its role inmediating the endocytosis of cargos at the plasmamembrane,m2YELLOW FLUORESCENT PROTEIN localized to transient foci at the plasmamembrane, and loss of m2 resulted in defects in bulk endocytosis. Furthermore, loss ofm2 led to increased accumulation of YELLOWFLUORESCENTPROTEIN-CESA6 particles at the plasmamembrane. Our results suggest that CESA represents a new class of CME cargo proteins and that plant cells might regulate cellulose synthesis by controlling the abundance of active CESA complexes at the plasma membrane through CME.