Analysis of transcripts and proteins expressed in the salivary glands of Hessian fly (Mayetiola destructor) larvae

Hessian fly (Mayetiola destructor) larvae are thought to manipulate host growth and metabolism through salivary secretions. However, the transcriptome and proteome of Hessian fly salivary glands have not been systematically analyzed. In this research, we analyzed Expressed-Sequence-Tags (EST) representing 6106 cDNA clones randomly selected from four libraries made from dissected salivary glands. We also analyzed the protein composition of dissected salivary glands using one- and two-dimensional gel electrophoresis as well as LC-MS/MS analysis. Transcriptomic analysis revealed that approximately 60% of the total cDNA clones and 40% of assembled clusters encoded secretory proteins (SP). The SP-encoding cDNAs were grouped into superfamilies and families according to sequence similarities. In addition to the high percentage of SP-encoding transcripts, there was also a high percentage of transcripts encoding proteins that were either involved directly in protein synthesis or in house-keeping functions that provide conditions necessary for protein synthesis. Proteomic analysis also revealed a high percentage of proteins involved in protein synthesis either directly or indirectly. The high percentage of SP-encoding transcripts and high percentage of proteins related to protein synthesis suggested that the salivary glands of Hessian fly larvae are indeed specialized tissues for synthesis of proteins for host injection. However, LC-MS/MS analysis of 64 proteins did not identify any SPs corresponding to the cDNA sequences. The lack of accumulation of SPs in the salivary glands indicated the SPs were likely secreted as soon as they were synthesized.