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Plant Physiol. 2018 Dec 13. pii: pp.01228.2018. doi: 10.1104/pp.18.01228. [Epub ahead of print]

A Golgi-released subpopulation of the trans-Golgi network mediates protein secretion in Arabidopsis.

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Ochanomizu University CITY: Tokyo POSTAL_CODE: 112-8610 Japan [JP]
Max Planck Institute for Plant Breeding Research CITY: Cologne POSTAL_CODE: 50829 Germany [DE].
Konan University CITY: Konan Japan [JP].
Max Planck Institute for Plant Breeding Research CITY: Cologne Germany [DE].
University of Muenster CITY: Muenster POSTAL_CODE: 48149 Germany [DE].
National Institute for Basic Biology CITY: Okazaki Japan [JP].
Max Planck Institute for Plant Breeding Research CITY: D-50829 Köln POSTAL_CODE: n/a Germany [DE].
RIKEN CITY: Saitama POSTAL_CODE: 351-0198 Japan [JP].


Spatiotemporal coordination of protein trafficking between organelles is essential for eukaryotic cells, and the post-Golgi interface, including the trans-Golgi network (TGN), is a pivotal hub for multiple trafficking pathways. The Golgi-released independent TGN (GI-TGN) is a compartment described only in plant cells, and its cellular and physiological roles remain elusive. In Arabidopsis thaliana, the SYP4 group Qa-SNARE (soluble N-ethyl-maleimide sensitive factor attachment protein receptor) membrane fusion proteins are shared components of TGN and GI-TGN and regulate secretory and vacuolar transport. Here we reveal that GI-TGNs mediate the transport of the R-SNARE VAMP721 to the plasma membrane. In interactions with a non-adapted powdery mildew pathogen, the SYP4 group of SNAREs is required for the dynamic relocation of VAMP721 to plant-fungus contact sites via GI-TGNs, thereby facilitating complex formation with its cognate SNARE partner PEN1 to restrict pathogen entry. Furthermore, quantitative proteomic analysis of leaf apoplastic fluid revealed constitutive and pathogen-inducible secretion of cell wall-modification enzymes in a SYP4- and VAMP721-dependent manner. Hence, the GI-TGN acts as a transit compartment between the Golgi apparatus and PM. We propose a model in which the GA-TGN matures first into the GI-TGN and then into secretory vesicles by increasing the abundance of VAMP721-dependent secretory pathway components.

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