Molecular intimacy between proteins specifying plant-pathogen recognition

Disease resistance in plants is commonly specified by genetically paired plant resistance (R) and pathogen avirulence (Avr) proteins. Recent molecular analyses of several R-Avr protein interactions provide compelling evidence for a receptor-ligand mechanism in which specific binding of the Avr elicitor by its matching R protein leads to activation of the plant defence response. Direct R-Avr protein recognition precedes the function of an expanding battery of plant resistance signalling components.