title: Characterisation of aphid proteins as targets for aphid control
Creators: name: Irving, Philabeg
Publisher: name: University of Glasgow
Year: 1998
Subjects: subject: Entomology

description: There have been extensive investigations of allozymes in aphid species, but only a relatively small amount of variation has been found between and, especially, within species. While modern molecular methods have shown that there is a large amount of variation amongst and within aphid species at the DNA level, there has been no concomitant detailed investigation of protein variation. 2DE was used as a powerful method to analyse the protein complement of aphid tissues. When the protein profiles of remnant and gut tissues were compared within and between several aphid species, higher levels of conservation were found in remnant tissue proteins than in the gut tissue proteins. These conservation levels may indicate different evolutionary processes in the two tissue types. The remnant proteins may have specific functions across all aphid species, which restrict the chances of accumulating mutations. The gut proteins do not appear to be similarly constrained, with the wide variation in gut protein profiles observed amongst aphid species possibly related to differences in their host ranges. The presence of protein homologues or common precursor molecules was indicated where some protein appeared to have slight, but distinct, differences between the species. The protein data from both tissues was qualitatively analysed to produce parsimonious comparisons between the aphid species. The gut protein data gave strong relationships between the species, which were in agreement with a classification based on aphid morphometries. However, the high level of conservation in the remnant proteins appeared to have obscured any separation of the species using this data. The effects of changing diet on the proteins of the aphid gut were also explored using 2DE. Within each clone, and therefore within each species, a small subset of proteins varied with host plant. On both host plant species, an analysis of this variation found that the changes included both additions and absences within the aphid gut protein profile. A polyclonal antiserum was raised against total proteins from M. persicae, fed on Chinese cabbage. The cross-reactivity of anti- whole M. persicae antiserum with large numbers of Western blotted proteins from other aphid species confirmed the protein conservation observed after 2DE protein analysis. A second polyclonal antiserum, raised against gut proteins from M persicae fed on Chinese cabbage, also showed cross-reactivity with Western blotted proteins from other aphid species. Probing with lectins, which specifically bind to secondary carbohydrate structures, showed that many of these cross-reacting gut proteins were glycosylated. As has been found with some antisera raised against proteins from other insects, the secondary carbohydrate structure of the proteins may account for some of the cross-reactivity seen with proteins from other species. The cross-reactivity of the anti-gut antibody may also indicate the presence of homologous proteins occurring in the guts of aphid species, previously indicated after 2DE separation and silver staining of aphid proteins. After establishing a suitable artificial diet for the long term culture of M. persicae, the effects of including the polyclonal antisera raised against aphid proteins in the diet were assessed. Inclusion of anti- M. persicae gut antiserum in artificial diet had a detrimental effect on the longevity of feeding aphids. The findings of the thesis are discussed in context of aphid control and the current trend towards in planta methods.