EXPRESSION OF TWO DEFENSE-RESPONSE GENES, HFR-1 AND WCI-1, UNDER BIOTIC AND ABIOTIC STRESSES

¹ Department of Entomology, Purdue University, 901 W. State St., West Lafayette, IN 47907, USA

² USDA-ARS Crop Production and Pest Control Research Unit, MWA, West Lafayette, IN 47907, USA

Two related defense-response genes (68% amino acid and 83% mRNA sequence identity),Hfr-1 (Hessian fly-response gene 1) and Wci-1 (Wheat chemically-induced gene 1) have been previously identified in wheat as responsive to Hessian fly infestation and SAR-inducer BTH (benzothiadiazole) treatment, respectively. Using Northern analyses and quantitative real-time PCR, we have compared the expression profiles of Hfr-1 and Wci-1 under biotic and abiotic stresses, and treatment with chemical elicitors of signaling pathways. Hessian fly infestation increased the expression of both Hfr-1 and Wci-1 at the larval feeding site (tissue between the root-shoot junction and the first ligule), with some systemic induction in leaf tissue. Results revealed similar expression profiles for both the genes, however, the transcript level of Hfr-1 was much higher as compared to that of Wci-1. In response to Bird Cherry-Oat aphid infestation, vector for barley yellow dwarf and cereal yellow dwarf virus, Wci-1 was up-regulated, while Hfr-1 did not show differential regulation. Wounding resulted in increased accumulation of Wci-1 mRNA but not of Hfr-1, whereas water stress increased Hfr-1 but not Wci-1 transcripts. Known global signaling molecules salicylic acid, abscisic acid and methyl jasmonate increased Wci-1 but not Hfr-1 expression, though both the genes were up-regulated by BTH treatments. Thus, despite high sequence homology, it appears that Hfr-1 and Wci-1 are up-regulated through different signaling pathways. The expression analyses indicate that Hfr-1 regulation is specific to the defense mechanisms elicited by feeding of first-instar Hessian fly larvae, while Wci-1 is probably a general defense-response gene differentially regulated by most of the biotic and abiotic stresses investigated.