What happened to plant caspases?

Area of Science:

• Cellular Biology
• Biochemistry

Background:

• Programmed cell death (PCD) pathways show varying conservation across kingdoms.
• Caspases are central to animal apoptosis, and similar activities are observed in plants.
• Plants possess caspase-like activities but lack direct caspase gene orthologs.

Purpose of the Study:

• To investigate the conservation of programmed cell death pathways across different species.
• To understand the nature and origin of caspase-like activities in plants.
• To identify plant proteases responsible for caspase-like activities.

Main Methods:

• Assaying caspase activities in plant extracts using synthetic substrates.
• Utilizing caspase inhibitors to block plant programmed cell death.
• Identifying specific proteases, such as vacuolar processing enzyme and saspase, involved in substrate cleavage.

Main Results:

• At least eight distinct caspase-like activities have been detected in plant extracts.
• Caspase inhibitors effectively block various forms of plant PCD.
• Vacuolar processing enzyme (a legumain) cleaves caspase-1 substrates, and saspase (a serine protease) cleaves caspase-8 and caspase-6 substrates.

Conclusions:

• Plant programmed cell death relies on caspase-like protease activities.
• The identified proteases (legumain and serine protease) are responsible for specific caspase-like activities in plants.
• The evolutionary relationship between plant caspase-like activities and animal caspases remains an open question, with plants lacking direct orthologs.