Comparative Transcriptomics Involving Greenbug and Water-Deficit Stress Responses in Hard-Red Winter Wheat

Plants have developed sophisticated mechanisms to precisely identify the nature of biotic and abiotic stresses and trigger cascade of relevant cellular signals that result in altered events in molecular and cellular homeostasis, ultimately, whole-plant physiology and growth.  However, despite the abundance of transcriptomic, proteomic, and metabolomic data in wheat, there is very little information about the parallels or contrasts between biotic and abiotic stress mechanisms at molecular level.  In the current study, we have integrated the transcriptomic data generated in response to greenbug (Schizaphis graminum) infestation and water-deficit stress in hard-red winter wheat.  The objectives of this study are to identify the patterns in gene expressions that are unique to greenbug and drought stress and that are common to both.  We used Affymetrix GeneChip Wheat Genome arrays for two independent transcriptomic studies and GeneSpring v.12 for data analysis.  Following normalization, a multivariate ANOVA and Benjamini Hochberg false discovery rate (P<0.01) resulted in 21612 and 26833 differentially regulated transcripts for water-deficit stress and greenbug feeding, respectively.  A joint analysis on transcripts with more than two fold change (5896 and 9301 for drought and greenbug respectively) categorized genes unique to greenbug feeding (6300), water-deficit stress (2895) and that were common to both (3001).  Functional analysis identified the role of hormone, secondary metabolites, stress-signaling, cell wall modification, heat shock protein, and proteolysis related transcripts in mediating defense responses.