Figure 1.

A schematic view of the two-tiered plant immune system. Recognition of PAMPs like bacterial flagellin and fungal chitin or DAMPs like secreted small peptides by PRRs induces intracellular signaling, leading to PTI. Successful pathogens deliver effector proteins (red dots) into the plant cell to dampen PTI. In some host plants, effector proteins are specifically recognized by the intracellular NLR immune receptors via different strategies, inducing effector-triggered immunity (ETI) that includes expression of immune-related genes and localized cell death referred to as HR. X, a host molecule guarded by NLRs; ID, integrated domain.