Transcriptional profiling reveals elevated CO₂ and elevated O₃ alter resistance of soybean (Glycine max) to Japanese beetles (Popillia japonica)

The accumulation of CO₂ and O₃ in the troposphere alters phytochemistry which in turn influences the interactions between plants and insects. Using microarray analysis of field-grown soybean (Glycine max), we found that the number of transcripts in the leaves affected by herbivory by Japanese beetles (Popillia japonica) was greater when plants were grown under elevated CO₂, elevated O₃ and the combination of elevated CO₂ plus elevated O₃ than when grown in ambient atmosphere. The effect of herbivory on transcription diminished strongly with time (<1% of genes were affected by herbivory after 3 weeks), and elevated CO₂ interacted more strongly with herbivory than elevated O ₃. The majority of transcripts affected by elevated O₃ were related to antioxidant metabolism. Constitutive levels and the induction by herbivory of key transcripts associated with defence and hormone signalling were down-regulated under elevated CO₂; 1-aminocyclopropane-1- carboxylate (ACC) synthase, lipoxygenase (LOX), allene oxide synthase (AOS), allene oxide cyclase (AOC), chalcone synthase (CHS), polyphenol oxidase (PPO) and cysteine protease inhibitor (CystPI) were lower in abundance compared with levels under ambient conditions. By suppressing the ability to mount an effective defence, elevated CO₂ may decrease resistance of soybean to herbivory.