title: The APG8/12-activating enzyme APG7 is required for proper nutrient recycling and senescence in Arabidopsis thaliana.
abstract: The vacuole/lysosome serves an important recycling function during starvation and senescence in eukaryotes via a process called autophagy. Here bulk cytosolic constituents and organelles become sequestered in specialized autophagic vesicles, which then deliver their cargo to the vacuole for degradation. In yeasts, genetic screens have identified two novel post-translational modification pathways remarkably similar to ubiquitination that are required for autophagy. From searches of the Arabidopsis genome, we have identified gene families encoding proteins related to both the APG8 and -12 polypeptide tags and orthologs for all components required for their attachment. A single APG7 gene encodes the ATP-dependent activating enzyme that initiates both conjugation pathways. Phenotypic analysis of an APG7 disruption indicates that it is not essential for normal growth and development in Arabidopsis. However, the apg7-1 mutant is hypersensitive to nutrient limiting conditions and displays premature leaf senescence. mRNAs for both APG7 and APG8 preferentially accumulate as leaves senesce, suggesting that both conjugation pathways are up-regulated during the senescence syndrome. These findings show that the APG8/12 conjugation pathways have been conserved in plants and may have important roles in autophagic recycling, especially during situations that require substantial nitrogen and carbon mobilization.
authors.affiliation: Cellular and Molecular Biology Program and the Department of Horticulture, University of Wisconsin, Madison, Wisconsin 53706, USA.
authors.forename: Jed H
authors.initials: JH
authors.lastname: Doelling
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Walker
authors.forename: Eric M
authors.initials: EM
authors.lastname: Friedman
authors.forename: Allison R
authors.initials: AR
authors.lastname: Thompson
authors.forename: Richard D
authors.initials: RD
authors.lastname: Vierstra
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins; D002244:Carbon / Q000378:metabolism; D016922:Cellular Senescence; D002734:Chlorophyll / Q000378:metabolism; D005656:Fungal Proteins / Q000502:physiology*; D017353:Gene Deletion; D005816:Genetic Complementation Test; D018745:Genome, Plant; D015151:Immunoblotting; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D008954:Models, Biological; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009154:Mutation; D009584:Nitrogen / Q000378:metabolism; D010641:Phenotype; D010802:Phylogeny; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D011506:Proteins / Q000378:metabolism*; D011523:Protoplasts / Q000378:metabolism; D012313:RNA / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid; D013997:Time Factors; D015854:Up-Regulation; D044764:Ubiquitin-Activating Enzymes
chemical_list: D000255:Adenosine Triphosphate; D029681:Arabidopsis Proteins; D002244:Carbon; D002734:Chlorophyll; D005656:Fungal Proteins; D008869:Microtubule-Associated Proteins; D009584:Nitrogen; D011506:Proteins; D012313:RNA; D012333:RNA, Messenger; D029701:Saccharomyces cerevisiae Proteins; C491970:APG7 protein, Arabidopsis; D044764:Ubiquitin-Activating Enzymes; C491896:APG8a protein, Arabidopsis; C491895:APG8i protein, Arabidopsis