Insect egg-induced innate immunity: Who benefits?

Abstract

Plants perceive the presence of insect eggs deposited on leaves as a cue of imminent herbivore attack. Consequential plant signaling events include the accumulation of salicylic acid and reactive oxygen species, transcriptional reprogramming, and cell death. Interestingly, egg-induced innate immunity shows similarities with immune responses triggered upon recognition of microbial pathogens, and in recent years, it became apparent that egg perception affects plant-microbe interactions. Here, we highlight recent findings on insect egg-induced innate immunity and how egg-mediated signaling impacts plant-microbe interactions. Ecological considerations beg the question: Who benefits from egg perception in these complex interactions?

Fig 1. Insect egg-triggered immunity affects plant–microbe interactions in Arabidopsis.

Arabidopsis plants perceive egg deposition and respond with a local induction of innate immunity. Emission of leaf volatiles leads to the attraction of egg parasitoids, which impedes egg survival. Activated signaling events lead to an increased resistance in the full plant foliage against microbial pathogens with different lifestyles including the bacterial plant pathogen Pseudomonas syringae, the fungal plant pathogen Botrytis cinerea, and the oomycete pathogen Hyaloperonospora arabidopsidis. Induction of this egg-induced SAR fully depends on SA and NHP signals and, surprisingly, also takes place in neighboring plants via yet unknown root-derived signal(s) (grey arrow). Interestingly, larvae of the specialist herbivore Pieris brassicae perform less well when feeding on plants infected with P. syringae and B. cinerea, indicating that activation of SAR in response to oviposition could be a strategy to ensure a healthy host plant to feed hatching larvae. NHP, N-hydroxypipecolic acid; SA, salicylic acid; SAR, systemic acquired resistance.