Pattern-recognition receptors are required for NLR-mediated plant immunity

Area of Science:

• Plant immunity
• Molecular plant-microbe interactions
• Plant cell signaling

Background:

• Plants possess a two-tiered innate immune system: pattern-triggered immunity (PTI) and effector-triggered immunity (ETI).
• PTI is activated by cell surface pattern-recognition receptors (PRRs), while ETI is mediated by intracellular nucleotide-binding, leucine-rich repeat receptors (NLRs).
• Distinct activation mechanisms and signaling cascades have been traditionally associated with PTI and ETI.

Purpose of the Study:

• To investigate the interplay between PTI and ETI signaling pathways in Arabidopsis.
• To determine the role of PRR components in ETI responses.
• To elucidate the molecular mechanisms connecting PRR and NLR signaling.

Main Methods:

• Utilized Arabidopsis mutants deficient in PRR and PRR co-receptors (fls2 efr cerk1 and bak1 bkk1 cerk1).
• Challenged mutants with incompatible Pseudomonas syringae bacteria to assess ETI.
• Analyzed the role of NADPH oxidase RBOHD and receptor-like cytoplasmic kinase BIK1 in immune signaling.

Main Results:

• PRR and co-receptor mutants showed impaired ETI responses.
• Reactive oxygen species (ROS) production by RBOHD is a key signaling event linking PRR and NLR immunity.
• BIK1 is essential for RBOHD activation, gene expression, and bacterial resistance during ETI.
• NLR signaling enhances PTI component levels during ETI.

Conclusions:

• Potentiation of PTI is an essential part of ETI during bacterial infections in plants.
• This revised model integrates PTI and ETI signaling, explaining shared downstream defense outputs.
• The findings provide a unified mechanistic understanding of plant innate immunity.