Effector proteins of phytopathogens recognized by intracellular immune receptors NB-LRR/NLR that activate second line of defence of the plant immune system

Abstract

The effector proteins employ common as well as pathogen-specific strategies to disturb plant immunity and to promote pathogen survival and favor their multiplication. However, in some cases, pathogen effectors are recognized by plant intracellular immune receptors NB-LRR/NLR that identify effector proteins, either directly by physical interaction or indirectly through monitoring of host proteins modification. NB-LRR immune receptors are characterized by the central nucleotide binding domain NB-ARC, C-terminal Leucine-Rich Repeats (LRRs) domain, and N-terminal TIR, CC or CCR domain. Immune receptors localized to the nucleus appears to be more directly associated with transcriptional regulation of defence gene expression, while the detection of pathogen effectors by membrane- or cytoplasm-localized immune receptors NB-LRR activate calcium-mediated signaling, ion flow, mitogen-activated protein kinase cascades, oxidative burst, biosynthesis of plant defence hormones and antimicrobial compounds, as well, far-reaching transcriptional reprogramming. Effector-triggered immunity normally culminates in programmed cell death called hypersensitive response (HR).