Endocytosis-mediated entry of a caterpillar effector into plants is countered by Jasmonate

Abstract Both insects and pathogens release effectors that are transferred into plant cells and weaken the host defense or immune response. While the imports of some bacterial and fungal effectors into plants have been reported, how caterpillar effectors enter plant cells remains a mystery. Here, using live cell imaging and real-time protein tracking, we show that HARP1, an effector from oral secretions of cotton bollworm (Helicoverpa armigera) which is previously reported to interfere with defense hormone jasmonate (JA) signaling output in host plants, enters plant cells via protein-mediated endocytosis. The interactions of HARP1 with vesicle trafficking components including CTL1, PATL2 and TET8 are essential for its entry. Notably, JA restricts HARP1 import by inhibiting endocytosis and HARP1 loading on endosomes. Taken together, the effector and JA set up a defense and counter-defense loop in the arm race between plants and insects. Our study unveils a new paradigm for the plant-insect interaction.