Abstract
The secreted salivary proteins from two cereal aphid species, Sitobion avenae and Metopolophium dirhodum, were collected from artificial diets and analysed by tandem mass spectrometry. Protein identification was performed by searching MS data against the official protein set from the current pea aphid (Acyrthosiphon pisum) genome assembly and revealed 12 and 7 proteins in the saliva of S. avenae and M. dirhodum, respectively. When combined with a comparable dataset from A. pisum, only three individual proteins were common to all the aphid species; two paralogues of the GMC oxidoreductase family (glucose dehydrogenase; GLD) and ACYPI009881, an aphid specific protein previously identified as a putative component of the salivary sheath. Antibodies were designed from translated protein sequences obtained from partial cDNA sequences for ACYPI009881 and both saliva associated GLDs. The antibodies detected all parent proteins in secreted saliva from the three aphid species, but could only detect ACYPI009881, and not saliva associated GLDs, in protein extractions from the salivary glands. This result was confirmed by immunohistochemistry using whole and sectioned salivary glands, and in addition, localised ACYPI009881 to specific cell types within the principal salivary gland. The implications of these findings for the origin of salivary components and the putative role of the proteins identified are discussed in the context of our limited understanding of the functional relationship between aphid saliva and the plants they feed on. The mass spectrometry data have been deposited to the ProteomeXchange and can be accessed under the identifier PXD000113.
Highlights
Insects that feed on living prey rely on bioactive compounds present in their saliva to negate the defences of their host
We identify salivary proteins secreted into chemically-defined diets by Sitobion avenae (Fabricius, 1775) and Metopolophium dihrodum (Walker, 1849), two aphid species that are important agricultural pests of cereals in Europe [17,18]
LC-MS/MS and Protein Identification Mass spectrometry data searched against the official protein set of A. pisum using the TurboSEQUEST algorithm resulted in the identification of 12 (46 peptides) and 7 (40 peptides) proteins in the saliva of S. avenae and M. dirhodum, respectively (Figure 1; Table 1 and Table 2)
Summary
Insects that feed on living prey rely on bioactive compounds present in their saliva to negate the defences of their host. The saliva of animal and plant feeding insects alike comprises a diverse suite of proteins that suppress, circumvent, modulate and even induce host defence and immune responses. Whilst the saliva of blood feeding insects has been extensively studied, due in part to their role as vectors of mammalian disease e.g. Aphids (Hemiptera: Aphidoidea) are phytophagous insects that feed on the phloem sap of plants. They are unusual herbivores because their feeding site is a single phloem cell in the sieve element buried deep within plant tissues, yet they represent one of the most important insect pests of temperate agriculture [4,5]. Aphid feeding reduces plant fitness by removing photoassimilates, transmitting plant viruses and, in some cases, altering plant growth and development [6]
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