Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/2/2008
Publication Date: 10/8/2008
Citation: Saltzmann, K.D., Giovanini, M., Zheng, C., Williams, C.E. 2008. Virulent Hessian Fly Larvae Manipulate the Free Amino Acid Content of Host Wheat Plants. Journal of Chemical Ecology. 34:1401-1410. Interpretive Summary: Little is known about mechanisms of resistance involved in interactions between wheat and the Hessian fly. Hessian fly larvae cause their host plants to produce increased levels of specific amino acids that are beneficial to larval development. Some of these amino acids that increase in abundance are essential for insects since they can’t make them but must receive them from their diet. Others are used for cuticle formation when the larvae pupate. And yet another amino acid is a rich source of stored energy. This is important because it suggests target process to be manipulated in the plant in order to increase resistance. Increased resistance will benefit farmers.
Technical Abstract: Virulent Hessian fly larvae induce their host wheat plants to provide a favorable environment for larval development by altering plant gene expression and promoting the formation of nutritive tissue at larval feeding sites. To determine whether Hessian fly larvae manipulate the nutrient content of their host plants, free amino acid levels were quantified in seedling crown tissue one, four and seven days after egg hatch. Hessian fly-infested susceptible plants were more responsive than resistant or control plants, showing a marked increase in total amino acid concentration four days after egg hatch. The largest increases in amino acid abundance were seen with alanine, aspartate, glutamate, glutamine, glycine, histidine, methionine, phenylalanine, proline, and serine. This four day post-hatch time point corresponds to the maturation of nutritive tissue in susceptible plants and the onset of rapid larval growth. By seven days after egg hatch, when virulent second-instar larvae are actively feeding on the contents of nutritive cells in susceptible host plants, the aromatic amino acids phenylalanine and tyrosine were significantly more abundant compared to uninfested controls, but the levels of other amino acids were no longer elevated. Changes in amino acid abundance described in this report were associated with increased levels of mRNA encoded by wheat genes involved in amino acid synthesis and transport.