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Title: Transcriptomics of induced defense responses to greenbug aphid feeding in near isogenic wheat lines

Author
item REDDY, S - Texas A&M University
item Weng, Yiqun
item RUDD, JACKIE - Texas A&M University
item AKHUNOVA, ALINA - Kansas State University
item LIU, RUDD - Kansas State University

Submitted to: Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/2/2013
Publication Date: 8/2/2013
Publication URL: http://handle.nal.usda.gov/10113/57729
Citation: Reddy, S.K., Weng, Y., Rudd, J.C., Akhunova, A., Liu, R.S. 2013. Transcriptomics of induced defense responses to greenbug aphid feeding in near isogenic wheat lines. Plant Science. 212:26-36.

Interpretive Summary: The greenbug aphid, Schizaphis graminum (Rondani) is an important cereal pest periodically threatening wheat yields in the United States and around the world. The wheat breeding program at Texas A&M University has introgressed the greenbug resistance gene Gb3 from synthetic wheat ‘Largo’ into the widely grown cultivars TAM 110 and TAM 112; however, the molecular mechanisms of Gb3-induced defense responses remain unknown. Using Affymetrix GeneChip Wheat Genome Arrays, we investigated the temporal dynamics of Gb3-mediated transcriptional responses upon greenbug feeding on resistant and susceptible bulks (RB and SB respectively) derived from two near-isogenic lines. Following statistical analysis, the MapMan functional classification on 692 differentially expressed transcripts from the interaction group identified 122 transcripts that were putatively associated with biotic stress responses. In RB, Gb3 induced transmembrane receptor kinases and downstream early defense signal transduction pathways. However, non-Gb3 mediated pathways in SB prompted induction of transcripts mediating callose decomposition and transcripts regulating biosynthesis of stress hormones jasmonic acid, ethylene, and abscisic acid. Additionally, the SB showed elevated levels of transcripts mediating redox homeostasis, peroxidases, glutathione S-transferases, and defense-related secondary metabolites. Overall, the results indicated that greenbugs inflicted more damage in the SB compared to RB and absence of Gb3-mediated signaling resulted in cell wall remodeling and strong accumulation of toxic compounds warranting production of antioxidant and relateddefense compounds. The study reinforced our knowledge about preferential feeding on S genotypes and plausible antixenosis or tolerance-related defense signaling in Gb3-associated R genotypes while paving the way for several new hypotheses.

Technical Abstract: The greenbug is an important cereal pest periodically threatening wheat yields in the United States and around the world. Although the greenbug resistance gene Gb3 has been widely deployed in wheat cultivars in the southern High Plains (for example, TAM 110 and TAM 112), the molecular mechanisms of Gb3-induced defense responses remain unknown. Using Affymetrix GeneChip Wheat Genome Arrays, we investigated the temporal dynamics of Gb3-mediated transcriptional responses upon greenbug feeding on resistant and susceptible bulks (RB and SB respectively) derived from two near-isogenic lines. Following statistical analysis, the MapMan functional classification on 692 differentially expressed transcripts from the interaction group identified 122 transcripts that were putatively associated with biotic stress responses. In RB, Gb3 induced transmembrane receptor kinases and downstream early defense signal transduction pathways. However, non-Gb3 mediated pathways in SB prompted induction of transcripts mediating callose decomposition and transcripts regulating biosynthesis of stress hormones jasmonic acid, ethylene, and abscisic acid. Additionally, the SB showed elevated levels of transcripts mediating redox homeostasis, peroxidases, glutathione S-transferases, and defense-related secondary metabolites. Overall, the results indicated that greenbugs inflicted more damage in the SB compared to RB and absence of Gb3-mediated signaling resulted in cell wall remodeling and strong accumulation of toxic compounds warranting production of antioxidant and relateddefense compounds. The study reinforced our knowledge about preferential feeding on S genotypes and plausible antixenosis or tolerance-related defense signaling in Gb3-associated R genotypes while paving the way for several new hypotheses.