Poltergeist-Like 2 (PLL2)-dependent activation of herbivore defence distinguishes systemin from other immune...

Systemin, the first signalling peptide identified in plants, mediates induced resistance against insect herbivores and necrotrophic pathogens in tomato^1-3. Initially, systemin was conceived as a hormone-like, long-distance messenger that triggers systemic defence responses far from the site of insect attack. It was later found to rather act as a phytocytokine, amplifying the local wound response for the production of downstream signals that activate defence gene expression in distant tissues⁴. Systemin perception and signalling rely on the systemin receptor SYR1⁵. However, the specifics of SYR1-dependent signalling and how systemin signalling differs from other immune signalling pathways remain largely unknown. Here we report that systemin activates the poltergeist-like phosphatase PLL2 in a SYR1-dependent manner. PLL2, in turn, regulates early systemin responses at the plasma membrane, including the rapid inhibition of proton pumps through dephosphorylation of their regulatory C-termini. PLL2 was found to be essential for downstream defence gene induction, ultimately contributing to insect resistance.