The primary interface between an aphid and its host plant is its saliva. The protein components of aphid saliva, the salivary secretome, are thought to interact with the plant in a similar manner to those secreted by prokaryotic and eukaryotic plant pathogens. Hence, a primary role of aphid saliva is to condition the plant for successful feeding by avoiding or suppressing plant cellular defences. However, the recognition of secreted aphid salivary proteins by plants also forms an integral part of the plant’s resistance response. The Russian wheat aphid (RWA) has rapidly evolved to overcome resistant varieties of wheat deployed widely in the United States of America and South Africa as part of response strategies to this highly-destructive pest.
The aims of our projects on RWA are to:
Taking advantage of the recently sequenced pea aphid genome, we have used a combined transcriptomics and proteomics approach to identify 65 proteins that have strong evidence supporting their expression and secretion into pea aphid saliva. This salivary secretome from pea aphid shows strong similarities to that of the plant pathogenic nematode Meloidogyne incognita. We have to date identified 21 of these pea aphid salivary proteins in Russian wheat aphid. A high level of diversity exists in many of these salivary proteins. High rates of salivary gland gene evolution have been achieved by gene duplication and diversifying selection. Some single copy salivary gland genes are also undergoing positive selection. Future studies will determine the relative frequency and distribution of salivary gland gene diversity in regions where RWA is endemic compared to those where RWA has recently invaded.