Any intracellular plant protein that acts as a receptor for a specific effector molecule released into the cell by invading bacteria, fungi, or other pathogens. Binding of an effector to its R protein receptor triggers a signal transduction pathway that activates effector-triggered immunity (see immunity sense 2) to combat the infection. R proteins are encoded by resistance (R) genes, while their corresponding effectors (or virulence factors) are encoded by Avirulence (Avr) genes in the respective pathogen. For example, a rust fungus that carries a particular Avr gene will induce an effective immune response in a variety of wheat having the corresponding R gene. Hence the desire of plant breeders to create crop varieties carrying R genes.