Proteomic analysis of the salivary glands of the rice brown planthopper, Nilaparvata lugens (Stal) (Homoptera: Delphacidae)

The rice brown planthopper, Nilaparvata lugens is a phloem-feeding insect pest of the rice plant Oryza sativa. To understand the role of saliva in its feeding process, we analyzed salivary gland proteins using two-dimensional polyacrylamide gel electrophoresis followed by Edman degradation of proteins. Of the 52 major spots analyzed, 25 N-terminal sequences were determined. The internal amino acid sequences of the remaining 27 proteins were determined by the Cleveland peptide mapping method. We identified 22 of the 25 proteins whose N-terminal regions were sequenced and 13 of the 27 proteins that were internally sequenced after searching them against the entries in the expressed sequence tag (EST) database of N. lugens. Through a homology search using public nonredundant protein databases, we identified EST-unmatched proteins. As a result, many housekeeping proteins responsible for energy metabolism, protein synthesis, folding and modification were identified, of which actins, tubulins, heat-shock proteins, protein disulfide isomerases and ATP synthases were in common with proteins identified from the salivary glands of hematophagous arthropods such as Anopheles gambiae, and a phytophagous gall midge Mayetiola destructor. However, we could not identify the glucosidases and phenoloxidases previously detected in the salivary glands of N. lugens. In contrast, novel proteins with an EF-hand domain were found in relatively high abundance in salivary gland homogenates derived from N. lugens; their corresponding ESTs were specifically derived from the salivary glands. Their calcium-binding properties suggest their importance of phloem feeding by the planthopper.