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McGinness AJ, Schoberer J, Pain C, Brandizzi F, Kriechbaumer V. On the nature of the plant ER exit sites. Front Plant Sci 2022; 13:1010569. [PMID: 36275575 PMCID: PMC9585722 DOI: 10.3389/fpls.2022.1010569] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/03/2022] [Accepted: 09/14/2022] [Indexed: 06/16/2023]
Abstract
In plants, the endoplasmic reticulum (ER) and Golgi bodies are not only in close proximity, but are also physically linked. This unique organization raises questions about the nature of the transport vectors carrying cargo between the two organelles. Same as in metazoan and yeast cells, it was suggested that cargo is transported from the ER to Golgi cisternae via COPII-coated vesicles produced at ribosome-free ER exit sites (ERES). Recent developments in mammalian cell research suggest, though, that COPII helps to select secretory cargo, but does not coat the carriers leaving the ER. Furthermore, it was shown that mammalian ERES expand into a tubular network containing secretory cargo, but no COPII components. Because of the close association of the ER and Golgi bodies in plant cells, it was previously proposed that ERES and the Golgi comprise a secretory unit that travels over or with a motile ER membrane. In this study, we aimed to explore the nature of ERES in plant cells and took advantage of high-resolution confocal microscopy and imaged ERES labelled with canonical markers (Sar1a, Sec16, Sec24). We found that ERES are dynamically connected to Golgi bodies and most likely represent pre-cis-Golgi cisternae. Furthermore, we showed fine tubular connections from the ER to Golgi compartments (ERGo tubules) as well as fine protrusions from ERES/Golgi cisternae connecting with the ER. We suggest that these tubules observed between the ER and Golgi as well as between the ER and ERES are involved in stabilizing the physical connection between ER and ERES/Golgi cisternae, but may also be involved in cargo transport from the ER to Golgi bodies.
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Affiliation(s)
- Alastair J. McGinness
- Endomembrane Structure and Function Research Group, Department of Biological and Medical Sciences, Oxford Brookes University, Oxford, United Kingdom
| | - Jennifer Schoberer
- Department of Applied Genetics and Cell Biology, Institute of Plant Biotechnology and Cell Biology, University of Natural Resources and Life Sciences, Vienna, Austria
| | - Charlotte Pain
- Endomembrane Structure and Function Research Group, Department of Biological and Medical Sciences, Oxford Brookes University, Oxford, United Kingdom
| | - Federica Brandizzi
- MSU-DOE Plant Research Lab, Michigan State University, East Lansing, MI, United States
- Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI, United States
- Department of Plant Biology, Michigan State University, East Lansing, MI, United States
| | - Verena Kriechbaumer
- Endomembrane Structure and Function Research Group, Department of Biological and Medical Sciences, Oxford Brookes University, Oxford, United Kingdom
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Urai Y, Yamawaki M, Watanabe N, Seki Y, Morimoto T, Tago K, Homma K, Sakagami H, Miyamoto Y, Yamauchi J. Pull down assay for GTP-bound form of Sar1a reveals its activation during morphological differentiation. Biochem Biophys Res Commun 2018; 503:2047-2053. [PMID: 30078678 DOI: 10.1016/j.bbrc.2018.07.157] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2018] [Accepted: 07/31/2018] [Indexed: 10/28/2022]
Abstract
The intracellular molecular transport system is a basic and general cellular mechanism that is regulated by an array of signaling molecules. Sar1 small GTPases are molecules that play a key role in controlling vehicle transport between the endoplasmic reticulum (ER) and Golgi bodies. Like other small GTPases, the activities of Sar1a depend on their guanine-nucleotide-binding states, which are regulated by guanine-nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs). Despite the well-known function of mammalian Sar1 in the intracellular transport system, little is known about when and how Sar1 is activated during cell morphological changes. Here we show that the C-terminal, but not the N-terminal, regions of Sec23A and Sec23B, the effector proteins of Sar1a, specifically bind to the active, GTP-bound form of Sar1a. An affinity precipitation (pull-down) assay using a recombinant C-terminal region of Sec23B reveals that Sar1a is activated following differentiation in neuronal cell lines. In neuronal N1E-115 cells, GTP-bound Sar1a is increased when cells elongate neuronal processes. Similar results are observed in morphological differentiation in oligodendroglial FBD-102b cells. Additionally, prolactin regulatory element binding (PREB), the GEF for Sar1 (Sar1 activator), increases the binding ability to the nucleotide-free form of Sar1a when morphological differentiation occurs. Nucleotide-free small GTPases preferentially interact with the cognate, active GEFs. These results provide evidence that using previously unreported pull down assays reveals that Sar1 and PREB are upregulated following the induction of morphological differentiation, suggesting the potential role of signaling through Sar1a during morphological differentiation.
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Affiliation(s)
- Yuri Urai
- Laboratory of Molecular Neuroscience and Neurology, Tokyo University of Pharmacy and Life Sciences, Hachioji, Tokyo, 192-0392, Japan
| | - Minami Yamawaki
- Laboratory of Molecular Neuroscience and Neurology, Tokyo University of Pharmacy and Life Sciences, Hachioji, Tokyo, 192-0392, Japan
| | - Natsumi Watanabe
- Laboratory of Molecular Neuroscience and Neurology, Tokyo University of Pharmacy and Life Sciences, Hachioji, Tokyo, 192-0392, Japan
| | - Yoich Seki
- Laboratory of Molecular Neuroscience and Neurology, Tokyo University of Pharmacy and Life Sciences, Hachioji, Tokyo, 192-0392, Japan
| | - Takako Morimoto
- Laboratory of Molecular Neuroscience and Neurology, Tokyo University of Pharmacy and Life Sciences, Hachioji, Tokyo, 192-0392, Japan
| | - Kenji Tago
- Division of Structural Biochemistry, Jichi Medical University, Shimotsuke, Tochigi, 329-0498, Japan
| | - Keiichi Homma
- Department of Life Science and Informatics, Maebashi Institute of Technology, Maebashi, Gunma, 371-0816, Japan
| | - Hiroyuki Sakagami
- Department of Anatomy, Kitasato University School of Medicine, Sagamihara, Kanagawa, 252-0734, Japan
| | - Yuki Miyamoto
- Laboratory of Molecular Neuroscience and Neurology, Tokyo University of Pharmacy and Life Sciences, Hachioji, Tokyo, 192-0392, Japan; Department of Pharmacology, National Research Institute for Child Health and Development, Setagaya, Tokyo, 157-8535, Japan
| | - Junji Yamauchi
- Laboratory of Molecular Neuroscience and Neurology, Tokyo University of Pharmacy and Life Sciences, Hachioji, Tokyo, 192-0392, Japan; Department of Pharmacology, National Research Institute for Child Health and Development, Setagaya, Tokyo, 157-8535, Japan.
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