Christopher Culbertson, Chemistry
Gerald Reeck, Biochemistry

From a physiological standpoint, the proteins and enzymes of the salivary secretions of aphids are known
to be crucial to an aphid’s feeding on a host plant and to establishing or influencing the aphid’s hostrange.
But at a biochemical level, we have virtually no direct information about the secretome. In this
proposal, which sets the scene for a variety of future investigations of individual proteins and enzymes of
aphid saliva, we propose a three-part approach to identifying individual components of the salivary
secretome of the pea aphid (Acyrthosiphon pisum). The three aspects of the proposed work correspond to
three levels of genetic information: the genome itself; transcripts from the genome; the proteins encoded
by those transcripts. At the genomic level, we will work in collaboration with colleagues in Australia to
computationally identify a whole-organism secretome. From that we will then examine individual
predicted proteins and tentatively identify proteins that are in the salivary secretome (by matches with
salivary ESTs from other species). At the transcript level, we will analyze some 10,000 ESTs from our
salivary cDNA libraries and, by matching to the corresponding gene sequences, identify those that contain
signals for extracellular secretion and hence can be tentatively assigned to the salivary secretome.
Finally, at the protein level, we will combine microfluidics (to obtain relatively undiluted salivary
secretions) and mass-spectrometry proteomics to directly identify proteins in the secretome (using the pea
aphid genome to interpret our data). The three approaches, in combination, should give a vastly improved
definition of the pea aphid secretome, which, in turn, will be used in future work as the basis for RNAi
knockdown of individual transcripts (to identify proteins of clear functional importance) and for
comparisons of the secretomes of aphid subspecies with distinct host-ranges.