Chloroplast signaling and reactive oxygen species generation in plant responses to aphids

The chloroplast, the organelle responsible for photosynthesis, is perturbed by many stresses including insect attack, and these perturbations can act as early warning system, triggering plant defense signaling. For example, in response to high light stress, chloroplasts accumulate excess levels of the reactive oxygen species (ROS) singlet oxygen, which reprograms nuclear gene expression and promotes stress adaptation by activating the EXECUTER1/EXECUTER2 (EX1/EX2) signaling pathway. However, very few studies have investigated whether such retrograde signaling plays a role in plant-insect interactions, and very little is known about the role of singlet oxygen in biotic stress in general. We utilized the interaction between the green peach aphid (Myzus persicae) and Arabidopsis (Arabidopsis thaliana) as a model system to explore the potential impacts of chloroplastic ROS signaling on plant responses to aphids. Here, we present evidence that aphids induce an oxidative response in the chloroplast, that enhanced ¹O₂ accumulation is correlated with aphid resistance in two different Arabidopsis genotypes, and that EX1/EX2 signaling contributes to defenses against aphids. We also assessed plant development and photosynthetic activity to explore possible tradeoffs between growth and defense. Our results reveal a new role for singlet oxygen and retrograde signaling in plant defense against insects.