During the plantemicrobe co-evolution, plants have evolved resistance proteins that specifically recognize effectors delivered into the plant cell by the successful pathogens. The recognition
leads to the activation of the second layer of immunity in plants termed ETI that usually culminates in HR, a programmed cell death that contains the invaded pathogen at the infection site [56,57]. Many R proteins have been characterized, most of which fall into the superfamily of nucleotide-binding (NB) leucine-rich repeat(LRR) proteins. Quite a few of the characterized R proteins have been identified to recognize their cognate Avr effectors directly or indirectly, leading to the proposition of direct and guard/decoy/bait models, respectively [1,58,59]. The direct recognition is evidenced by several R proteins that physically interact with their cognate