Submitted to: Plant Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/10/2005
Publication Date: 1/6/2006
Citation: Subramanyam, S., Sardesai, N., Puthoff, D.P., Meyer, J.M., Gonzalo, M., Williams, C.E. 2006. Expression of two wheat defense-response genes, Hfr-1 and Wci-1, under biotic and abiotic stresses. Plant Science. 170:90-103. Interpretive Summary: Little is known about mechanisms of resistance involved in interactions between wheat and the Hessian fly. We characterized two closely related wheat genes that are up-regulated when the plant is attacked by Hessian fly larvae. One appears to be a general stress-response gene that is involved in defense against aphids, virus and wounding, whereas the other gene is more specific in its response to the Hessian fly. These genes have never before been implicated as involved in defense against insects and will be useful to scientists and plant breeders wanting to use lectin genes in resistance strategies.
Technical Abstract: We previously reported a Hessian fly-responsive wheat gene (Hfr-1), which is up-regulated during incompatible interactions. This gene showed high sequence identity to a wheat chemically-induced gene (Wci-1). Here we analyze the temporal expression of these genes under biotic and abiotic stresses, as well as during treatments with the global signaling molecules, salicylic acid (SA), benzothiadiazole (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 elicited 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 nonviruliferous and viruliferous bird cherry-oat aphids, Wci-1 was up-regulated, while Hfr-1 did not show differential regulation. SA and BTH treatments elevated transcript levels of both genes, whereas MeJa and ABA up-regulated only Wci-1. When leaves were mechanically wounded, Wci-1 mRNA accumulated but Hfr-1 did not, while water-deficit stress increased Hfr-1, but not Wci-1 transcripts. 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 regulation is specific to defense mechanisms elicited by feeding of Hessian fly larvae, while Wci-1 shows characteristics of a general defense-response gene in most of the biotic and abiotic stresses we investigated.