VPEgamma exhibits a caspase-like activity that contributes to defense against pathogens.
BACKGROUND
Caspases are a family of aspartate-specific cysteine proteases that play an essential role in initiating and executing programmed cell death (PCD) in metazoans. Caspase-like activities have been shown to be required for the initiation of PCD in plants, but the genes encoding those activities have not been identified. VPEgamma, a cysteine protease, is induced during senescence, a form of PCD in plants, and is localized in precursor protease vesicles and vacuoles, compartments associated with PCD processes in plants.


RESULTS
We show that VPEgamma binds in vivo to a general caspase inhibitor and to caspase-1-specific inhibitors, which block the activity of VPEgamma. A cysteine protease inhibitor, cystatin, accumulates to 20-fold higher levels in vpegamma mutants. Homologs of cystatin are known to suppress hypersensitive cell death in plant and animal systems. We also report that infection with an avirulent strain of Pseudomonas syringae results in an increase of caspase-1 activity, and this increase is partially suppressed in vpegamma mutants. Plants overexpressing VPEgamma exhibit a greater amount of ion leakage during infection with P. syringae, suggesting that VPEgamma may regulate cell death progression during plant-pathogen interaction. VPEgamma expression is induced after infection with P. syringae, Botrytis cinerea, and turnip mosaic virus, and knockout of VPEgamma results in increased susceptibility to these pathogens.


CONCLUSIONS
We conclude that VPEgamma is a caspase-like enzyme that has been recruited in plants to regulate vacuole-mediated cell dismantling during cell death, a process that has significant influence in the outcome of a diverse set of plant-pathogen interactions.
Rojo
Enrique
E
Departamento de Genética Molecular de Plantas, Centro Nacional de Biotecnología, Consejo Superior de Investigaciones Cientificas, E-28049 Madrid, Spain. erojo@cnb.uam.es
Martín
Raquel
R
Carter
Clay
C
Zouhar
Jan
J
Pan
Songqin
S
Plotnikova
Julia
J
Jin
Hailing
H
Paneque
Manuel
M
Sánchez-Serrano
José Juan
JJ
Baker
Barbara
B
Ausubel
Frederick M
FM
Raikhel
Natasha V
NV
D017209:Apoptosis / Q000502:physiology*; D017360:Arabidopsis / Q000201:enzymology* / Q000382:microbiology; D020171:Botrytis; D020169:Caspases / Q000378:metabolism*; D015891:Cystatins / Q000378:metabolism; D003546:Cysteine Endopeptidases / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D017931:DNA Primers; D004198:Disease Susceptibility / Q000382:microbiology / Q000821:virology; D018506:Gene Expression Regulation, Plant; D009154:Mutation / Q000235:genetics; D010935:Plant Diseases / Q000382:microbiology / Q000821:virology; D044224:Pseudomonas syringae; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017806:Tymovirus
D015891:Cystatins; D017931:DNA Primers; D020169:Caspases; D003546:Cysteine Endopeptidases; C098280:vacuolar processing enzyme gamma, Arabidopsis