Double‐Edged Sword Effect of Jasmonoyl‐Isoleucine on the Parasite–Host Interaction Between Field Dodder and Lentil

ABSTRACT Many holoparasitic plants are well‐known for their negative impacts on crops, yet the underlying mechanisms behind the interaction between holoparasitic plants and their hosts are still poorly understood. This study investigates the role of stress‐induced phytohormones on the relationship between field dodder ( Cuscuta campestris ) and lentil plants ( Lens culinaris ), a model for parasitic plant‐host interaction in legumes. We evaluated the impact of parasitism on host phenology, vegetative growth, and yield. In addition, stress markers and spatiotemporal variations in endogenous levels of stress‐related phytohormones were measured. Parasitism had a drastic effect on yield by accelerating plant phenology, enhancing plant senescence, and deregulating pod maturation. Moreover, an antagonistic relationship between jasmonates and abscisic acid (ABA) was observed in field dodder during the attachment of haustoria to the host, such that the content of the bioactive jasmonate, jasmonoyl‐isoleucine (contrary to ABA), was very high in free haustoria (prior to attachment). Finally, the content of jasmonoyl‐isoleucine increased in the host plant, although this defense response in young leaves was not sufficient to prevent severe loss of PSII integrity. This demonstrates that jasmonoyl‐isoleucine is up‐regulated in both free‐haustoria field dodder and infested lentil plants, suggesting that this bioactive jasmonate form has a universal protective role in both sides of the interaction between parasitic plant and host.