Salivary proteins of Russian wheat aphid (Hempitera: Aphididae)

Authors: Cooper, William - Rodney; DILLWITH, JACK - Oklahoma State University; Puterka, Gary

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/16/2009
Publication Date: 2/1/2010
Citation: Cooper, W.R., Dillwith, J.W., Puterka, G.J. 2010. Salivary proteins of Russian wheat aphid (Hempitera: Aphididae). Environmental Entomology. 39(1):223-231.

Interpretive Summary: Aphid saliva play critical roles in insect – plant interactions and is responsible for damage associated with aphid feeding. Aphids secrete two types of saliva: the stylet sheath and watery saliva. The Russian wheat aphid is a global pest of small grains that causes leaf yellowing, leaf rolling, and plant mortality. Salivary proteins were isolated and compared from aphid probed diets consisting of either water, 15% sucrose, or amino acids (100 mM serine, 100 mM methionine, 100 mM aspartic acid, and 15% sucrose). After 6 hrs, more aphids settled on sucrose diet compared to other diets, but there were no significant differences in the number of stylet sheaths produced per aphid after 24 hrs. There were differences in the amount of watery saliva, with the greatest amount secreted in sucrose diet, followed by amino acid diet and pure water. We also found qualitative differences between saliva collected from sucrose and amino acid diets. Enzyme phosphatase was putatively identified from D. noxia saliva from a major protein band using SDS-PAGE and mass spectrophotometry and confirmed in sucrose diet using enzymatic assays, but was not detected in aphid probed water or amino acid diets. Other peptides putatively identified were dehydrogenase and RNA helicase. More work is required to discover potential roles of these proteins in plant – insect interactions.

Technical Abstract: Salivary secretions play critical roles in aphid – host plant interactions and are responsible for damage associated with aphid feeding. The objectives of this study were to evaluate aspects of salivation and the salivary constituents of Diuraphis noxia (Hemiptera: Aphididae). Salivary proteins were isolated and compared from three aphid probed diets, namely pure water, 15% sucrose, or amino acids (100 mM serine, 100 mM methionine, 100 mM aspartic acid, and 15% sucrose). After 6 hrs, more aphids settled on sucrose diet compared to other diets, but there were no significant differences in the number of stylet sheaths produced per aphid after 24 hrs. There were differences in the amount of soluble salivary protein (watery saliva), with the greatest amount secreted in sucrose diet, followed by amino acid diet and pure water, respectively. Protein constituents secreted into sucrose and amino acid diets were compared on SDS-PAGE using standardized amounts of protein. More protein bands and bands of greater intensity were visualized from probed sucrose diet compared to probed amino acid diet indicating qualitative differences. Phosphatase was putatively identified from D. noxia saliva from a major protein band using SDS-PAGE and mass spectrophotometry. Alkaline phosphatase activity was confirmed in sucrose diet using enzymatic assays, but was not detected in aphid probed water or amino acid diets. Other peptides in sucrose diet weakly but significantly showed similarities to putative dehydrogenase and RNA helicase ESTs identified from other aphids. The implications of these findings in aphid salivation and plant – insect interactions are discussed.