title: A novel membrane fusion-mediated plant immunity against bacterial pathogens.
abstract: Plants have developed their own defense strategies because they have no immune cells. A common plant defense strategy involves programmed cell death (PCD) at the infection site, but how the PCD-associated cell-autonomous immunity is executed in plants is not fully understood. Here we provide a novel mechanism underlying cell-autonomous immunity, which involves the fusion of membranes of a large central vacuole with the plasma membrane, resulting in the discharge of vacuolar antibacterial proteins to the outside of the cells, where bacteria proliferate. The extracellular fluid that was discharged from the vacuoles of infected leaves had both antibacterial activity and cell death-inducing activity. We found that a defect in proteasome function abolished the membrane fusion associated with both disease resistance and PCD in response to avirulent bacterial strains but not to a virulent strain. Furthermore, RNAi plants with a defective proteasome subunit PBA1 have reduced DEVDase activity, which is an activity associated with caspase-3, one of the executors of animal apoptosis. The plant counterpart of caspase-3 has not yet been identified. Our results suggest that PBA1 acts as a plant caspase-3-like enzyme. Thus, this novel defense strategy through proteasome-regulating membrane fusion of the vacuolar and plasma membranes provides plants with a mechanism for attacking intercellular bacterial pathogens.
authors.affiliation: Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.
authors.forename: Noriyuki
authors.initials: N
authors.lastname: Hatsugai
authors.forename: Shinji
authors.initials: S
authors.lastname: Iwasaki
authors.forename: Kentaro
authors.initials: K
authors.lastname: Tamura
authors.forename: Maki
authors.initials: M
authors.lastname: Kondo
authors.forename: Kentaro
authors.initials: K
authors.lastname: Fuji
authors.forename: Kimi
authors.initials: K
authors.lastname: Ogasawara
authors.forename: Mikio
authors.initials: M
authors.lastname: Nishimura
authors.forename: Ikuko
authors.initials: I
authors.lastname: Hara-Nishimura
mesh_terms: D017209:Apoptosis; D017360:Arabidopsis / Q000276:immunology / Q000382:microbiology*; D020170:Caspase 1 / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D008561:Membrane Fusion; D010935:Plant Diseases / Q000382:microbiology*; D010940:Plant Proteins / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D044224:Pseudomonas syringae / Q000502:physiology*; D014617:Vacuoles / Q000378:metabolism*
chemical_list: D010940:Plant Proteins; D020170:Caspase 1; D046988:Proteasome Endopeptidase Complex