Genomic insights into the serine protease gene family and expression profile analysis in the planthopper, Nilaparvata lugens.

Background: The brown planthopper (Nilaparvata lugens) is one of the most destructive rice plant pests in Asia. N. lugens causes extensive damage to rice by sucking rice phloem sap, which results in hopper burn (complete death of the rice plants). Despite its importance, little is known about the digestion, development and defense mechanisms of this hemimetabolous insect pest. In this study, we aim to identify the serine protease (SP) and serine protease homolog (SPH) genes, which form a large family in eukaryotes, due to the potential for multiple physiological roles. Having a fully sequenced genome for N. lugens allows us to perform in-depth analysis of the gene structures, reveal the evolutionary relationships and predict the physiological functions of SP genes.
Results: The genome- and transcriptome-wide analysis identified 90 putative SP (65) and SPH (25) genes in N. lugens. Detailed gene information regarding the exon-intron organization, size, distribution and transcription orientation in the genome revealed that many SP/SPH loci are closely situated on the same scaffold, indicating the frequent occurrence of gene duplications in this large gene family. The gene expression profiles revealed new findings with regard to how SPs/SPHs respond to bacterial infections as well as their tissue-, development- and sex-specific expressions.
Conclusions: Our findings provide comprehensive gene sequence resources and expression profiles of the N. lugens SP and SPH genes, which give insights into clarifying the potentially functional roles of these genes in the biological processes including development, digestion, reproduction and immunity.