Hypersensitive Response in Plants

Abstract The hypersensitive response (HR) is a type of programmed cell death, which is part of the plant's defence response against pathogen attack. In the best of cases, this strategy isolates the pathogens from nutrients during the early steps of infection, causing them to starve before they are able to cause damage. The ability to suppress HR is a major factor for determining whether a pathogen manages to successfully infect a plant. For this reason, HR represents a promising target for improving the overall resistance of crops against pathogens. Attempts to do so are, however, hampered by our lack of understanding how HR is regulated. Signals from the PAMP‐ and effector‐triggered immunity pathways, as well as ROS and phytohormone signals all converge on HR, making it a particularly difficult system to study. Key Concepts Hypersensitive response is highly complex because of the involvement of many actors. Because of HR, many pathogens starve before they can damage the plant. Signals from PTI, ETI, ROS and phytohormones converge on HR. HR is not an intracellular event, but instead receives input from distant tissues as well. In contrast to early findings, HR is not restricted to the ETI response. How ROS is involved in the HR signalling pathway is still not sufficiently understood. Hypersensitive response often serves as a first line of defence against pathogens, which overcome the preinvasion defences.