Activation of TIR signalling boosts pattern-triggered immunity.

Plant immune responses are mainly activated by two types of receptor. Plasma membrane-localized pattern recognition receptors (PRRs) perceive extracellular microbial features, and nucleotide-binding leucine-rich repeat receptors (NLRs) recognize intracellular effector proteins from pathogens1. NLRs possessing N-terminal Toll/interleukin-1 receptor (TIR) domains activate defence responses via the NADase activity of the TIR domain2,3. Here we report that activation of TIR signalling plays a key role in PRR-mediated pattern-triggered immunity (PTI). TIR signalling mutants exhibit attenuated PTI responses and decreased resistance against pathogens. Consistently, PTI is compromised in plants with reduced NLR levels. Treatment with PTI elicitor flg22 or nlp20 rapidly induces many genes encoding TIR domain-containing proteins, which is likely to be responsible for activating TIR signalling during PTI. Overall, our study reveals that TIR signalling activation is an important mechanism for boosting plant defence during PTI.