How Parasitic Plants weaken Host Immunity and facilitate Infections by Microbial Pathogens

Crop infestations by parasitic plants pose significant challenges to farmers, especially in resource-limited subsistence agriculture, resulting in lower yields and potential field abandonment. We asked if infestations by parasitic plants affect host immunity to microbial pathogens, potentially creating refugia for pathogens that could spread to uninfested plant communities. Studying the root parasitic model plant Phtheirospermum japonicum, we observed that immune responses in host shoots, including flg22- and chitin-induced reactive oxygen species production, defense gene expression, and mitogen-activated protein kinase phosphorylation, were strongly reduced in hosts parasitized by P. japonicum. The systemic immune-compromising effect caused by parasitism led to more growth of the microbial pathogens Pseudomonas syringae and Botrytis cinerea. Based on obtained RNA-Seq data, we propose that reduced nutrient availability for the host, changes in its hormone homeostasis, and potential effectors may contribute to the observed systemic suppression of host immunity. In conclusion, our study draws attention to the risk of parasitic infestations in increasing secondary microbial infections, with implications for crop protection and disease management.