Expression of two wheat defense-response genes, Hfr-1 and Wci-1, under biotic and abiotic stresses

Wheat plants respond to attack by Hessian fly in a gene-for-gene manner resulting in either a compatible or an incompatible interaction depending on the genotype of the infesting larvae. We previously reported a Hessian fly-responsive wheat gene (Hfr-1), up-regulated during incompatible interactions, that showed high sequence identity to a wheat gene (Wci-1) known to be induced by benzothiadiazole (BTH). Here, we analyze the temporal expression of these genes under biotic (Hessian fly/aphid/virus) and abiotic (mechanical wounding/water-deficit) stresses, as well as during treatments with the global signaling molecules, salicylic acid (SA), BTH, methyl jasmonate (MeJa) and abscisic acid (ABA) using northern hybridization and quantitative real-time PCR. Virulent Hessian fly infestation increased the expression of both Hfr-1 and Wci-1 in the crown tissue, while low systemic induction was observed in the leaf blade tissue. Although both genes were up-regulated to higher levels during incompatible interactions in multiple wheat genotypes, Hfr-1 transcripts accumulated to a higher level than Wci-1 transcripts. In response to infestation by non-viruliferous and viruliferous bird cherry-oat aphids, Wci-1 was up-regulated, while Hfr-1 was not. SA and BTH treatments up-regulated both genes, whereas MeJa and ABA up-regulated only Wci-1. When leaves were mechanically wounded, Wci-1 mRNA was up-regulated but Hfr-1 was not, while water-deficit stress up-regulated Hfr-1, but not Wci-1. Our results show that despite high sequence identity, Hfr-1 and Wci-1 exhibit differential expression profiles in response to various stresses and are regulated through separate signaling pathways. Hfr-1 responds to defense mechanisms elicited by feeding of Hessian fly larvae and water stress, while Wci-1 shows characteristics of a general defense-response gene in most of the biotic and abiotic stresses we investigated. (c) 2005 Elsevier Ireland Ltd. All rights reserved.