Oviposition by Pierid Butterflies Triggers Defense Responses in Arabidopsis

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Abstract
Insect eggs represent a threat for the plant as hatching larvae rapidly start with their feeding activity. Using a whole-genome microarray, we studied the expression profile of Arabidopsis (Arabidopsis thaliana) leaves after oviposition by two pierid butterflies. For Pieris brassicae, the deposition of egg batches changed the expression of hundreds of genes over a period of 3 d after oviposition. The transcript signature was similar to that observed during a hypersensitive response or in lesion-mimic mutants, including the induction of defense and stress-related genes and the repression of genes involved in growth and photosynthesis. Deposition of single eggs by Pieris rapae caused a similar although much weaker transcriptional response. Analysis of the jasmonic acid and salicylic acid mutants coi1-1 and sid2-1 indicated that the response to egg deposition is mostly independent of these signaling pathways. Histochemical analyses showed that egg deposition is causing a localized cell death, accompanied by the accumulation of callose, and the production of reactive oxygen species. In addition, activation of the pathogenesis-related1::beta-glucuronidase reporter gene correlated precisely with the site of egg deposition and was also triggered by crude egg extract. This study provides molecular evidence for the detection of egg deposition by Arabidopsis plants and suggests that oviposition causes a localized response with strong similarity to a hypersensitive response.