title: Arabidopsis μ-adaptin subunit AP1M of adaptor protein complex 1 mediates late secretory and vacuolar traffic and is required for growth.
abstract: Adaptor protein (AP) complexes are the predominant coat proteins of membrane vesicles in post-Golgi trafficking of mammalian cells. Each AP complex contains a specific medium subunit, μ-adaptin, that selects cargo proteins bearing sequence-specific sorting motifs. Much less is known about the AP complexes and their μ subunits in plants. Because of uncertain homology, the μ-adaptins of Arabidopsis have been designated muA through muD [Happel et al. (2004) Plant J 37(5):678-693]. Furthermore, only muD has been assigned to a specific AP complex, AP-3, involved in Golgi-vacuolar trafficking [Niihama et al. (2009) Plant Cell Physiol 50(12):2057-2068, Zwiewka et al. (2011) Cell Res 21(12):1711-1722, and Wolfenstetter et al. (2012) Plant Cell 24(1):215-232]. In contrast, the μ subunit of neither the post-Golgi trafficking AP-1 complex nor the endocytic AP-2 complex has been identified. Here, we report the functional analysis of redundant AP-1 μ-adaptins AP1M1 (also known as muB1) and AP1M2 (also known as muB2). Coimmunoprecipitation revealed that both AP1M2 and its less strongly expressed isoform AP1M1 are complexed with the large subunit γ-adaptin of AP-1. In addition, AP1M2 was localized at or near the trans-Golgi network. Knockout mutations of AP1M2 impaired pollen function and arrested plant growth whereas the ap1m1 ap1m2 double mutant was nearly pollen-lethal. At the cellular level, the absence of AP1M2 entailed inhibition of multiple trafficking pathways from the trans-Golgi network to the vacuole and to the plasma membrane in interphase and to the plane of cell division in cytokinesis. Thus, AP-1 is crucial in post-Golgi trafficking in plant cells and required for cell division and plant growth.
authors.affiliation: Entwicklungsgenetik and Microscopy, Zentrum für Molekularbiologie der Pflanzen (ZMBP), University of Tübingen, 72076 Tübingen, Germany.
authors.forename: Misoon
authors.initials: M
authors.lastname: Park
authors.forename: Kyungyoung
authors.initials: K
authors.lastname: Song
authors.forename: Ilka
authors.initials: I
authors.lastname: Reichardt
authors.forename: Hyeran
authors.initials: H
authors.lastname: Kim
authors.forename: Ulrike
authors.initials: U
authors.lastname: Mayer
authors.forename: York-Dieter
authors.initials: YD
authors.lastname: Stierhof
authors.forename: Inhwan
authors.initials: I
authors.lastname: Hwang
authors.forename: Gerd
authors.initials: G
authors.lastname: Jürgens
mesh_terms: D033961:Adaptor Protein Complex 1 / Q000235:genetics / Q000378:metabolism*; D033965:Adaptor Protein Complex alpha Subunits / Q000378:metabolism; D033982:Adaptor Protein Complex gamma Subunits / Q000378:metabolism; D033983:Adaptor Protein Complex mu Subunits / Q000235:genetics / Q000378:metabolism*; D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000502:physiology / Q000648:ultrastructure; D048749:Cytokinesis / Q000502:physiology; D006056:Golgi Apparatus / Q000378:metabolism / Q000648:ultrastructure; D007399:Interphase / Q000502:physiology; D046529:Microscopy, Electron, Transmission; D016254:Mutagenesis, Insertional; D021381:Protein Transport / Q000502:physiology*; D022142:Secretory Vesicles / Q000378:metabolism / Q000648:ultrastructure; D014617:Vacuoles / Q000378:metabolism / Q000648:ultrastructure; D021601:trans-Golgi Network / Q000378:metabolism / Q000648:ultrastructure
chemical_list: C583121:AP1M1 protein, Arabidopsis; C583122:AP1M2 protein, Arabidopsis; D033961:Adaptor Protein Complex 1; D033965:Adaptor Protein Complex alpha Subunits; D033982:Adaptor Protein Complex gamma Subunits; D033983:Adaptor Protein Complex mu Subunits; D029681:Arabidopsis Proteins; C499066:adaptor protein complex 1, mu 1 subunit; C499065:adaptor protein complex 1, mu 2 subunit
keywords: adaptor complex 1; development; membrane traffic; secretory pathway