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