Chloroplasts navigate towards the pathogen interface to counteract infection by the Irish potato famine pathogen

Chloroplasts are light harvesting organelles that arose from ancient endosymbiotic cyanobacteria. Upon immune activation, chloroplasts switch off photosynthesis, produce anti-microbial compounds, and develop tubular extensions called stromules. We report that chloroplasts navigate to the pathogen interface to counteract infection by the Irish potato famine pathogen Phytophthora infestans, physically associating with the specialised membrane that engulfs pathogen haustoria. Outer envelope protein, chloroplast unusual positioning1 (CHUP1), anchors chloroplasts to the host-pathogen interface. Stromules are induced during infection in a CHUP1-dependent manner, embracing haustoria and interconnecting chloroplasts, to form dynamic organelle clusters. Infection-triggered reprogramming of chloroplasts relies on surface immune signalling, whereas pathogen effectors subvert these immune pulses. Chloroplast are deployed focally, and coordinate to restrict pathogen entry into plant cells, a process actively countered by parasite effectors.