A plant caspase-like protease activated during the hypersensitive response

Area of Science:

• Plant molecular biology
• Cellular apoptosis mechanisms
• Plant-pathogen interactions

Background:

• Programmed cell death (PCD) is essential in plants, but the underlying proteases are not fully understood.
• The hypersensitive response (HR) is a form of pathogen-induced PCD in plants, often mediated by specific genes.
• Caspase-like proteases are known to be involved in PCD in animals, but their role in plants requires further investigation.

Purpose of the Study:

• To test the hypothesis that caspase-like proteases are involved in plant PCD.
• To identify and characterize plant caspases activated during the N gene-mediated HR in tobacco plants infected with Tobacco mosaic virus (TMV).

Main Methods:

• Used Agrobacterium tumefaciens VirD2 protein as a target substrate for detecting tobacco caspases.
• Analyzed proteolytic processing of VirD2 derivatives in tobacco leaves during TMV-triggered HR.
• Partially purified a plant proteolytic activity specific for a caspase cleavage site (TATD).
• Synthesized a tetrapeptide aldehyde inhibitor to block caspase activity.

Main Results:

• Specific proteolytic processing of VirD2 at TATD and GEQD sites occurred early in TMV-triggered HR in tobacco leaves.
• A plant proteolytic activity cleaving the TATD site was partially purified.
• The synthesized tetrapeptide aldehyde inhibited plant and human caspases in vitro.
• The inhibitor counteracted TMV-triggered HR in vivo, confirming the role of caspase-like activity.

Conclusions:

• Caspase-specific protein fragmentation occurs in plant apoptotic cells.
• This caspase-like activity is critically involved in the implementation of programmed cell death (PCD) in plants.
• The findings provide insights into the molecular mechanisms of plant PCD and potential targets for disease resistance.