Plants perceive pathogens and activate immunity using two very different types of receptors. Receptors at the cell surface detect pathogen-derived molecules that accumulate outside plant cells, activating pattern-triggered immunity (PTI). PTI is suppressed by pathogen-derived effector proteins, that are injected into host cells to enable pathogen growth, but these effectors can be detected by intracellular receptors, resulting in effector-triggered immunity (ETI). Until now, it has not been clear how the defense mechanisms activated by these two distinct perception mechanisms interact.
source https://phys.org/news/2021-03-immunity-requires-two-step-invaders.html
