Abstract
BackgroundSerine protease inhibitors (SPIs) have been found in all living organisms and play significant roles in digestion, development and innate immunity. In this study, we present a genome-wide identification and expression profiling of SPI genes in the diamondback moth, Plutella xylostella (L.), a major pest of cruciferous crops with global distribution and broad resistance to different types of insecticides.ResultsA total of 61 potential SPI genes were identified in the P. xylostella genome, and these SPIs were classified into serpins, canonical inhibitors, and alpha-2-macroglobulins based on their modes of action. Sequence alignments showed that amino acid residues in the hinge region of known inhibitory serpins from other insect species were conserved in most P. xylostella serpins, suggesting that these P. xylostella serpins may be functionally active. Phylogenetic analysis confirmed that P. xylostella inhibitory serpins were clustered with known inhibitory serpins from six other insect species. More interestingly, nine serpins were highly similar to the orthologues in Manduca sexta which have been demonstrated to participate in regulating the prophenoloxidase activation cascade, an important innate immune response in insects. Of the 61 P.xylostella SPI genes, 33 were canonical SPIs containing seven types of inhibitor domains, including Kunitz, Kazal, TIL, amfpi, Antistasin, WAP and Pacifastin. Moreover, some SPIs contained additional non-inhibitor domains, including spondin_N, reeler, and other modules, which may be involved in protein-protein interactions. Gene expression profiling showed gene-differential, stage- and sex-specific expression patterns of SPIs, suggesting that SPIs may be involved in multiple physiological processes in P. xylostella.ConclusionsThis is the most comprehensive investigation so far on SPI genes in P. xylostella. The characterized features and expression patterns of P. xylostella SPIs indicate that the SPI family genes may be involved in innate immunity of this species. Our findings provide valuable information for uncovering further biological roles of SPI genes in P. xylostella.
Highlights
Serine protease inhibitors (SPIs) have been found in all living organisms and play significant roles in digestion, development and innate immunity
A total of 61 putative SPI genes were identified in P. xylostella (Table 1 and Additional file 1: Table S1), and the deduced amino acid sequences were provided in Additional file 1: Table S2
The 61 putative SPI genes were classified into three types: serpins, canonical SPIs, and α2Ms (Table 1) based on their mechanisms of action
Summary
Serine protease inhibitors (SPIs) have been found in all living organisms and play significant roles in digestion, development and innate immunity. Serine proteases are ubiquitous enzymes in almost all organisms, from bacteria to mammals [1], and they are known to play significant roles in a wide range of biological processes [2,3,4,5]. Besides their crucial physiological roles, proteases carry out an unlimited number of hydrolytic reactions to break down proteins [6], and such proteolytic activity can be potentially hazardous in living systems. The non-canonical inhibitors interact with target proteases through their N-terminal segments, which are secondary interactions outside the active site to significantly enhance the affinity, velocity and specificity of recognition [7, 9]
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