News from the frontline: recent insights into PAMP-triggered immunity in plants

Plants have developed a complex defence network to fight off invading pathogens. In recent years, the full importance of pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) within this network became apparent. Several new PAMPs have been isolated and new pattern-recognition receptors (PRRs) identified. The discovery of the PRR-interacting protein BAK1 sheds light on the immediate downstream signalling events. Further, transcriptomic analyses identified a core set of ∼100 PAMP-responsive genes. These studies also revealed a significant overlap with genes regulated during effector-triggered immunity (ETI). Strikingly, ETI seems to operate by alleviating the negative feedback regulation of PTI, leading to stronger defences. This review discusses recent findings in PTI recognition and signalling, and illustrates the need to discover new regulators of PTI responses for a full understanding of plant innate immunity.