Submitted to: New Phytologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/12/2008
Publication Date: 4/1/2008
Citation: Li, Y., Zou, J., Li, M., Bilgin, D., Vodkin, L.O., Hartman, G.L., Clough, S.J. 2008. Soybean defense responses to the soybean aphid. New Phytologist. 179(1):185-195. Interpretive Summary: We identified gene expression differences between an aphid resistant and susceptible soybean cultivar. These expression differences were compared to the expression pattern of a strong resistance response known as the hypersensitive response or HR. This expression comparison suggests that the resistant soybean cultivar is activated to induce an HR within hours of aphid feeding and that this response is lacking in the susceptible cultivar. Genes that were associated with the resistance response will be further characterized to determine if they are associated with the single gene conferring the difference between resistance and susceptibility between these two cultivars. Identification of an aphid resistance gene would be of great interest to breeders and seed companies.
Technical Abstract: Transcript profiles in resistant (cv. Dowling) and susceptible (cv. Williams 82) soybean [Glycine max (L.) Merrill] genotypes were compared at 6 and 12 h with and without aphid (Aphis glycines Matsumura) infestation using cDNA microarrays. One hundred and sixteen genes showed specific responses in resistance and included genes related to signaling, DNA-binding, oxidation, defense, secondary metabolism and other processes. The expression data published on soybean response to hypersensitive response (HR) induced by Pseudomonas syringae at 8 h showed a high degree of similarity with aphid-induced responses in resistant plants at 6 and 12 h, suggesting an HR-like reaction might play a role in the aphid resistance in Dowling. Expression of three defense-related genes, soybean P21 (AW458142), MMP2 homolog (AW100655), and PR1a precursor homolog (BG511448), was examined at 6, 12, 24, 48, and 72 h in both genotypes by quantitative real-time PCR in separate experiment using aphid cages. The results indicated an earlier and greater abundance at 6, 12 and 24 h in resistance response, with transcript levels beginning to decline after 24 h or 48 h in resistance but continued to increase in susceptible after 24 h, which coincides with the observed aphid feeding behavior. In addition to identifying differences in transcript levels in response to aphids, five genes were also identified as differentially expressed genes between the two genotypes in the absence of aphids and may be candidates for aphid-resistance genes.