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. 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.adaptor complex 1 | membrane traffic | secretory pathway | development

Adaptor Protein Complex 2–Mediated Endocytosis Is Crucial for Male Reproductive Organ Development in Arabidopsis

“…Consistent with the biochemical and subcellular localization data, ap2m-1 plants exhibit a defect in endocytosis of FM4-64 in the filaments, which was phenocopied by the Tyrphostin A23 treatment of wild-type filaments. This finding is consistent with recent observations that mD is a component of AP-3 and AP1M1 (muB1) and AP1M2 (muB2) are components of AP-1 complexes (Happel et al, 2004;Niihama et al, 2009;Zwiewka et al, 2011, Park et al, 2013). Another piece of supporting evidence for AP2M as a component of AP-2 is that AP2A1 RNAi transgenic plants showed phenotypes that were similar to those of ap2m mutant plants in defects in seed production and phyllotaxis.…”

“…The Arabidopsis genome contains five m-adaptin homologs. Recently, it has been shown that muB1 (AP1M1) and muB2 (AP1M2) are m-adaptin subunits of AP-1 and mD is the m-adaptin subunit of AP-3 (Happel et al, 2004;Niihama et al, 2009;Zwiewka et al, 2011;Park et al, 2013). Sequence homology analysis revealed that AP2M (aka muA) displayed the highest sequence homology to the animal m2 of AP-2 (see Supplemental Figures 2A and 2B online), raising the possibility that AP2M is the m-adaptin subunit of AP-2 in Arabidopsis.…”

“…Subsequently, the AP2A1 RNAi construct in the pENTER vector was transferred to pHellgate8 with LR clonase (Invitrogen) to generate the pHellsgate-AP2A1 RNAi construct. The generation of the AP1M2:HAx3 construct was performed as described (Park et al, 2013).…”

Danger-associated peptide signaling in Arabidopsis requires clathrin

“…Given that the amounts of PEPR1-GFP and TAMRA-pep1 at the PM were not reduced after AX2 induction, we conclude that the secretion of PEPR1 is not significantly affected. In addition, the AtPep1-mediated MAPK activation was not altered by mutations in the medium subunit of the TGN/EE-localized AP-1, which is essential for post-Golgi trafficking (24). Despite their involvement in CME, the mutant alleles of AP-2, ap2m-2 and ap2s (21, 22), did not affect TAMRA-pep1 uptake or AtPep1-mediated MAPK activation, raising the question of whether PEPR endocytosis is mediated by AP-2.…”

Identification and Dynamics of Arabidopsis Adaptor Protein-2 Complex and Its Involvement in Floral Organ Development

“…AP-3 plays roles in post-Golgi trafficking and is involved in the regulation of vacuolar biogenesis (Niihama et al, 2009;Feraru et al, 2010;Zwiewka et al, 2011). AP-1 is required for trafficking of the cytokinesis-specific soluble N-ethylmaleimide-sensitive attachment protein receptor (SNARE) KNOLLE to the cell plate, which mediates proper cell division (Park et al, 2013;Teh et al, 2013). AP-1 also influences vascular development in the aerial tissues (Wang et al, 2013).…”