Abstract
Plant innate immunity begins with the recognition of pathogens by plasma membrane localized pattern-recognition receptors (PRRs) and intracellular nucleotide-binding domain leucine-rich repeat containing receptors (NLRs), which lead to pattern-triggered immunity (PTI) and effector-triggered immunity (ETI), respectively. For a long time, PTI and ETI have been regarded as two independent processes although they share multiple components and signal outputs. Increasing evidence shows an intimate link between PTI and ETI. PTI and ETI mutually potentiate each other, and this is essential for robust disease resistance during pathogen infection. An ancient class of NLRs called RNLs, so named because they carry a Resistance to Powdery Mildew 8 (RPW8)-like coiled-coil (CC) domain in the N terminus, has emerged as a key node connecting PTI and ETI. RNLs not only act as helper NLRs that signal downstream of sensor NLRs, they also directly mediate PTI signaling by associating with PRR complexes. Here, we focus on Activated Disease Resistance 1 (ADR1), a subclass of RNLs, and discuss its role and mechanism in plant immunity.