Monday, December 11, 2006 - 9:23 AM

Modulation of soybean, Glycine max defenses to herbivory by Japanese beetles (Popillia japonica ) under ambient and elevated atmospheric CO2

Clare L. Casteel, ccastee2@uiuc.edu1, Jorge Zavala,, May R. Berenbaum, maybe@uiuc.edu2, and Evan De Lucia, delucia@life.uiuc.edu3. (1) University of Illinois - Urbana/Champaign, Department of Plant Biology, Institute for Genomic Ecology, ASL 01, 1207 W. Gregory Ave, Urbana, IL, (2) University of Illinois - Urbana/Champaign, Department of Entomology, 505 S. Goodwin Ave, 320 Morrill Hall, Urbana, IL, (3) University of Illinois, Department of Plant Biology, 265 Morrill Hall, 505 South Goodwin Avenue, 320 Morrill Hall, 505 S. Goodwin Ave, Urbana, IL

Anthropogenic greenhouse gases are increasing in the troposphere and may alter plant-insect interactions in agro-ecosystems. Elevated CO2 increased Japanese beetle (Popillia japonica Newman) colonization and herbivory in soybean (Glycine max) agro-ecosystem, suggesting that elevated CO2 decreased plant defenses. To test this hypothesis and explain the mechanism behind it, we examined Japanese beetle herbivory at the soybean free-air concentration site (soyFACE), under conditions of either ambient or elevated CO2. The expression of over 40,000 transcripts after beetle attack was quantified in soybean leaves with Affymetrix microarrays and the accumulation of the hormone jasmonic acid (JA) and the defense compounds cysteine proteinase inhibitors (CystPI) determined. Interestingly, elevated CO2 down regulated the expression of genes related to JA and CystPI and decreased the accumulation of these products in the leaves. Elicitation of leaves by either beetle attack or methyl jasmonate application increased both transcripts and metabolites (JA and CystPI) accumulation, but with lower levels in plants grown in elevated than in ambient CO2. Furthermore, the activity of the digestive enzyme cysteine was lower in the guts of beetles that fed on plants grown under elevated than ambient CO2. Changes in tropospheric chemistry associated with global change thus modulates well-established transcriptional responses and allelochemicals that are important to plant defense, and may increase the susceptibility of soybean crops to insect herbivores in the future.

Species 1: Coleoptera Scarabaeidae Popillia japonica (Japanese beetle)