title: Aspartyl Protease-Mediated Cleavage of BAG6 Is Necessary for Autophagy and Fungal Resistance in Plants.
abstract: The Bcl-2-associated athanogene (BAG) family is an evolutionarily conserved group of cochaperones that modulate numerous cellular processes. Previously we found that Arabidopsis thaliana BAG6 is required for basal immunity against the fungal phytopathogen Botrytis cinerea. However, the mechanisms by which BAG6 controls immunity are obscure. Here, we address this important question by determining the molecular mechanisms responsible for BAG6-mediated basal resistance. We show that Arabidopsis BAG6 is cleaved in vivo in a caspase-1-like-dependent manner and via a combination of pull-downs, mass spectrometry, yeast two-hybrid assays, and chemical genomics, we demonstrate that BAG6 interacts with a C2 GRAM domain protein (BAGP1) and an aspartyl protease (APCB1), both of which are required for BAG6 processing. Furthermore, fluorescence and transmission electron microscopy established that BAG6 cleavage triggers autophagy in the host that coincides with disease resistance. Targeted inactivation of BAGP1 or APCB1 results in the blocking of BAG6 processing and loss of resistance. Mutation of the cleavage site blocks cleavage and inhibits autophagy in plants; disease resistance is also compromised. Taken together, these results identify a mechanism that couples an aspartyl protease with a molecular cochaperone to trigger autophagy and plant defense, providing a key link between fungal recognition and the induction of cell death and resistance.
authors.affiliation: Institute for Plant Genomics and Biotechnology, Texas A&M University, College Station, Texas 77843 Department of Plant Pathology and Microbiology, Texas A&M University, College Station, Texas 77843.
authors.forename: Yurong
authors.initials: Y
authors.lastname: Li
authors.affiliation: Department of Plant Pathology, University of Wisconsin-Madison, Madison, Wisconsin 53706.
authors.forename: Mehdi
authors.initials: M
authors.lastname: Kabbage
authors.affiliation: Institute for Plant Genomics and Biotechnology, Texas A&M University, College Station, Texas 77843.
authors.forename: Wende
authors.initials: W
authors.lastname: Liu
authors.affiliation: Institute for Plant Genomics and Biotechnology, Texas A&M University, College Station, Texas 77843 Department of Plant Pathology and Microbiology, Texas A&M University, College Station, Texas 77843 mbdickman@tamu.edu.
authors.forename: Martin B
authors.initials: MB
authors.lastname: Dickman
mesh_terms: D017360:Arabidopsis / Q000166:cytology* / Q000201:enzymology / Q000382:microbiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D057055:Aspartic Acid Proteases / Q000378:metabolism*; D001343:Autophagy; D020171:Botrytis / Q000254:growth & development / Q000502:physiology*; D020170:Caspase 1 / Q000378:metabolism; D060467:Disease Resistance; D006801:Humans; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010641:Phenotype; D010935:Plant Diseases / Q000382:microbiology; D030821:Plants, Genetically Modified; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D014026:Nicotiana / Q000235:genetics
chemical_list: D029681:Arabidopsis Proteins; C000611886:BAG6 protein, Arabidopsis; D018832:Molecular Chaperones; D009687:Nuclear Proteins; D057055:Aspartic Acid Proteases; D020170:Caspase 1