title: Processing of ATG8s, ubiquitin-like proteins, and their deconjugation by ATG4s are essential for plant autophagy.
abstract: Autophagy is an intracellular process for vacuolar degradation of cytoplasmic components. Thus far, plant autophagy has been studied primarily using morphological analyses. A recent genome-wide search revealed significant conservation among autophagy genes (ATGs) in yeast and plants. It has not been proved, however, that Arabidopsis thaliana ATG genes are required for plant autophagy. To evaluate this requirement, we examined the ubiquitination-like Atg8 lipidation system, whose component genes are all found in the Arabidopsis genome. In Arabidopsis, all nine ATG8 genes and two ATG4 genes were expressed ubiquitously and were induced further by nitrogen starvation. To establish a system monitoring autophagy in whole plants, we generated transgenic Arabidopsis expressing each green fluorescent protein-ATG8 fusion (GFP-ATG8). In wild-type plants, GFP-ATG8s were observed as ring shapes in the cytoplasm and were delivered to vacuolar lumens under nitrogen-starved conditions. By contrast, in a T-DNA insertion double mutant of the ATG4s (atg4a4b-1), autophagosomes were not observed, and the GFP-ATG8s were not delivered to the vacuole under nitrogen-starved conditions. In addition, we detected autophagic bodies in the vacuoles of wild-type roots but not in those of atg4a4b-1 in the presence of concanamycin A, a V-ATPase inhibitor. Biochemical analyses also provided evidence that autophagy in higher plants requires ATG proteins. The phenotypic analysis of atg4a4b-1 indicated that plant autophagy contributes to the development of a root system under conditions of nutrient limitation.
authors.affiliation: Department of Cell Biology, National Institute for Basic Biology, Myodaiji-cho, Okazaki 444-8585, Japan.
authors.forename: Kohki
authors.initials: K
authors.lastname: Yoshimoto
authors.forename: Hideki
authors.initials: H
authors.lastname: Hanaoka
authors.forename: Shusei
authors.initials: S
authors.lastname: Sato
authors.forename: Tomohiko
authors.initials: T
authors.lastname: Kato
authors.forename: Satoshi
authors.initials: S
authors.lastname: Tabata
authors.forename: Takeshi
authors.initials: T
authors.lastname: Noda
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Ohsumi
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D001343:Autophagy / Q000502:physiology*; D004269:DNA, Bacterial / Q000302:isolation & purification; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018507:Gene Expression Regulation, Developmental / Q000502:physiology; D018506:Gene Expression Regulation, Plant / Q000502:physiology; D005816:Genetic Complementation Test; D046529:Microscopy, Electron, Transmission; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D009584:Nitrogen / Q000378:metabolism; D018517:Plant Roots / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism*; D025262:Vacuolar Proton-Translocating ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism; D014617:Vacuoles / Q000235:genetics / Q000378:metabolism
chemical_list: C491896:APG8a protein, Arabidopsis; C491895:APG8i protein, Arabidopsis; D029681:Arabidopsis Proteins; D004269:DNA, Bacterial; D004791:Enzyme Inhibitors; D008869:Microtubule-Associated Proteins; D011993:Recombinant Fusion Proteins; C036483:T-DNA; D025801:Ubiquitin; D025262:Vacuolar Proton-Translocating ATPases; D009584:Nitrogen