Abstract
Communication between cellular organelles is essential for mounting effective innate immune responses to eliminate pathogens. In plants, the transport of cellular organelles to pathogen penetration sites and their assembly around the host membrane delineating plant-pathogen interface are well-documented. However, whether organelles associate with these specialized plant-pathogen membrane interfaces and the extent to which this process contributes to immunity remain unknown. Here, we discovered defense-related membrane contact sites (MCS) comprising a membrane tethering complex between chloroplasts and the extrahaustorial membrane (EHM) surrounding the pathogen haustorium. The assembly of this membrane tethering complex relies on the association between the chloroplast outer envelope protein CHLOROPLAST UNUSUAL POSITIONING 1 (CHUP1), and its plasma membrane-associated partner, KINESIN-LIKE PROTEIN FOR ACTIN-BASED CHLOROPLAST MOVEMENT 1 (KAC1). Our biochemical assays revealed that CHUP1 and KAC1 interact, while infection cell biology demonstrated their co-accumulation in foci where chloroplasts contact the EHM. Genetic depletion of CHUP1 or KAC1 reduces the deposition of callose—a cell wall material typically deployed to fortify pathogen penetration resistance—around the haustorium, without affecting other core immune processes. Our findings suggest that the chloroplast-EHM attachment complex positively regulates plant focal immunity, revealing the key components and their potential roles in the targeted deposition of defense components at the pathogen interface. These results advance our understanding of organelle-mediated immune responses and highlight the significance of MCS in plant-pathogen interactions.
Competing Interest Statement
T.B. and C.D. receive funding from industry on NLR biology. T.B. and C.D. are co-founders of Resurrect Bio Ltd. The remaining authors have no conflicts of interest to declare.
Footnotes
This version of the manuscript has been significantly revised to include many new findings. The original manuscript was summarized as "We discovered that CHUP1 is required for focal immunity against Phytophthora infestans," which represents only the initial part of the revised content. The revised manuscript can be summarized as "We discovered defense-related membrane contact sites (MCS) comprising a membrane tethering complex (CHUP1-KAC1) between chloroplasts and the extrahaustorial membrane surrounding the pathogen haustorium, which contributes to plant focal immunity."
