The APG8/12-activating Enzyme APG7 Is Required for Proper Nutrient Recycling and Senescence in Arabidopsis thaliana

• Published in: The Journal of biological chemistry 2002-09, Vol.277 (36), p.33105-33114
• Main Authors: Doelling, Jed H., Walker, Joseph M., Friedman, Eric M., Thompson, Allison R., Vierstra, Richard D.
• Format: Article
• Language: English
• Subjects: Adenosine Triphosphate - metabolism; Amino Acid Sequence; Arabidopsis - metabolism; Arabidopsis Proteins; Carbon - metabolism; Cellular Senescence; Chlorophyll - metabolism; Fungal Proteins - physiology; Gene Deletion; Genetic Complementation Test; Genome, Plant; Immunoblotting; Microtubule-Associated Proteins - metabolism; Models, Biological; Models, Genetic; Molecular Sequence Data; Mutation; Nitrogen - metabolism; Phenotype; Phylogeny; Protein Binding; Protein Processing, Post-Translational; Proteins - metabolism; Protoplasts - metabolism; RNA - metabolism; RNA, Messenger - metabolism; Saccharomyces cerevisiae Proteins; Sequence Homology, Amino Acid; Time Factors; Up-Regulation
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M204630200

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 Arabidopsisgenome, 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 APG7gene encodes the ATP-dependent activating enzyme that initiates both conjugation pathways. Phenotypic analysis of anAPG7 disruption indicates that it is not essential for normal growth and development in Arabidopsis. However, theapg7-1 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.