The hypersensitive response; the centenary is upon us but how much do we know?

Area of Science:

• Plant pathology
• Molecular biology
• Cellular processes

Background:

• The hypersensitive response (HR) is a key plant defense mechanism against pathogens.
• Recent decades have seen significant advancements in understanding HR initiation, signaling, and associated proteolysis.
• The centenary of HR's initial description necessitates a review of current knowledge.

Purpose of the Study:

• To assess the current understanding of the hypersensitive response (HR) as a form of plant cell death.
• To review progress in elucidating HR initiation, signaling pathways, and genetic components.
• To discuss the distinct nature of HR compared to mammalian apoptosis and explore potential roles of metabolic dysfunction.

Main Methods:

• Review of genetic approaches to identify HR-initiating resistance genes.
• Analysis of various death-associated signals including calcium, reactive oxygen species (ROS), nitric oxide, salicylic acid, and sphingolipids.
• Exploration of potential mechanisms involving metabolic dysfunction and organelle roles in HR.

Main Results:

• Extensive genetic analyses have identified key resistance genes involved in HR.
• Numerous signaling molecules (calcium, ROS, nitric oxide, salicylic acid, sphingolipids) have been implicated in HR.
• Parallels between HR and mammalian apoptosis have proven largely unsuccessful, suggesting HR is a distinct plant cell death process.

Conclusions:

• Significant knowledge exists regarding specific components of the HR.
• The HR is increasingly recognized as a unique form of plant cell death, potentially involving metabolic dysfunction.
• A comprehensive molecular model for the HR remains to be fully developed.