title: ATG9 regulates autophagosome progression from the endoplasmic reticulum in Arabidopsis.
abstract: Autophagy is a conserved pathway for bulk degradation of cytoplasmic material by a double-membrane structure named the autophagosome. The initiation of autophagosome formation requires the recruitment of autophagy-related protein 9 (ATG9) vesicles to the preautophagosomal structure. However, the functional relationship between ATG9 vesicles and the phagophore is controversial in different systems, and the molecular function of ATG9 remains unknown in plants. Here, we demonstrate that ATG9 is essential for endoplasmic reticulum (ER)-derived autophagosome formation in plants. Through a combination of genetic, in vivo imaging and electron tomography approaches, we show that Arabidopsis ATG9 deficiency leads to a drastic accumulation of autophagosome-related tubular structures in direct membrane continuity with the ER upon autophagic induction. Dynamic analyses demonstrate a transient membrane association between ATG9 vesicles and the autophagosomal membrane during autophagy. Furthermore, trafficking of ATG18a is compromised in atg9 mutants during autophagy by forming extended tubules in a phosphatidylinositol 3-phosphate-dependent manner. Taken together, this study provides evidence for a pivotal role of ATG9 in regulating autophagosome progression from the ER membrane in Arabidopsis.
authors.affiliation: Centre for Cell & Developmental Biology, School of Life Sciences, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China.|State Key Laboratory of Agrobiotechnology, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China.
authors.forename: Xiaohong
authors.initials: X
authors.lastname: Zhuang
authors.affiliation: Centre for Cell & Developmental Biology, School of Life Sciences, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China.|State Key Laboratory of Agrobiotechnology, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China.
authors.forename: Kin Pan
authors.identifier: 0000-0003-2786-3095
authors.initials: KP
authors.lastname: Chung
authors.affiliation: Centre for Cell & Developmental Biology, School of Life Sciences, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China.|State Key Laboratory of Agrobiotechnology, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China.
authors.forename: Yong
authors.initials: Y
authors.lastname: Cui
authors.affiliation: Centre for Cell & Developmental Biology, School of Life Sciences, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China.|State Key Laboratory of Agrobiotechnology, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China.
authors.forename: Weili
authors.initials: W
authors.lastname: Lin
authors.affiliation: Centre for Cell & Developmental Biology, School of Life Sciences, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China.|State Key Laboratory of Agrobiotechnology, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China.
authors.forename: Caiji
authors.initials: C
authors.lastname: Gao
authors.affiliation: Centre for Cell & Developmental Biology, School of Life Sciences, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China.|State Key Laboratory of Agrobiotechnology, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China.
authors.forename: Byung-Ho
authors.initials: BH
authors.lastname: Kang
authors.affiliation: Centre for Cell & Developmental Biology, School of Life Sciences, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China; ljiang@cuhk.edu.hk.|State Key Laboratory of Agrobiotechnology, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China.|The Chinese University of Hong Kong Shenzhen Research Institute, Shenzhen 518057, China.
authors.forename: Liwen
authors.initials: L
authors.lastname: Jiang
mesh_terms: D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D000071182:Autophagosomes / Q000378:metabolism*; D001343:Autophagy / Q000502:physiology; D000071183:Autophagy-Related Proteins / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism; D021381:Protein Transport / Q000502:physiology
chemical_list: C466979:APG9 protein, Arabidopsis; D029681:Arabidopsis Proteins; D000071183:Autophagy-Related Proteins; D002352:Carrier Proteins; D008565:Membrane Proteins; D018129:Phosphatidylinositol Phosphates; C055525:phosphatidylinositol 3-phosphate
keywords: ATG18; ATG9; autophagosome; autophagy; endoplasmic reticulum