Fig. 1.

Activation of plant immune system. A two-tiered immune system comprising pattern-triggered immunity (PTI) and effector-triggered immunity (ETI) occur in plants. The instant immune response is mediated by PRRs that triggers PTI whereas NLR activate ETI upon translocation of T3E into the cytoplasm via. T3SS. Signalling events by PRRs and NLRs leads to overlapping downstream cellular responses, including defense-gene expression, production of ROS and callose deposition. The primary plant immune receptors viz. PRRs and NLRs function synergistically to ensure a robust level of key immune components during ETI. SAR is induced when the ETI takes over the pathogenic effector and plants are able to resist secondary infection in uninfected parts of plants.