Submitted to: Plant Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2005
Publication Date: 6/1/2005
Citation: Puthoff, D.P., Sardesa, N., Subramanyam, S., Nemacheck, J.A., Williams, C.E. 2005. Hfr-2, a wheat cytolytic toxin-like gene up-regulated by virulent hessian fly larvae and armyworm feeding. Plant Molecular Biology. 6:411-423. Interpretive Summary: Little is known about which genes are important in defending plants against insect pests, and even less is known about ways that insects can hijack plant genes and use them against the plant in order to change the plant into a better host. We characterized a wheat gene that is used by Hessian fly larvae. This gene, Hfr-2 (Hessian fly responsive gene 2), is believed to specify a protein that can insert into wheat cells where the larva feeds and cause those cells to leak nutrients such as sugars, amino acids or small bits of protein and liquids. The larva is then able to consume these nutrients that normally would be locked up in the cell. Under normal conditions, the plant gene probably functions in defense by inserting into bacterial cells, causing them to burst. But the Hessian fly and a few other insects have found a way to use this gene against the plant itself for their own benefit.
Technical Abstract: Both grain yield and quality are dramatically decreased when susceptible wheat plants are infested by Hessian fly larvae. Examination of the changes in wheat gene expression during infestation by virulent Hessian fly larvae has identified up-regulation of a gene, Hessian fly responsive-2, (Hfr-2), which contains regions similar to genes encoding seed-specific proteins from Amaranthus. However, HFR-2 did not accumulate in developing seeds, as do other wheat seed storage proteins. Additionally, a separate region of the HFR-2 predicted amino acid sequence is similar to agglutinin proteins from Amaranthus and hemolytic proteins from both mushroom and bacteria. These two proteins are able to form pores in cell membranes of mammalian blood cells. The involvement of Hfr-2 in interactions with insects was supported by experiments demonstrating its up-regulation by both armyworm and aphid infestations but not by virus infection. Examination of wheat defense response pathways showed Hfr-2 up-regulation following methyl jasmonate treatment and only slight up-regulation in response to SA, ABA and wounding treatments. Although like related proteins, HFR-2 may function as in defense against pathogens, we propose that as virulent Hessian fly larvae manipulate the physiology of the susceptible host, HFR-2 proteins insert in plant cell membranes at the feeding sites and provide water, ions and other small nutritive molecules to the developing larvae.