Abstract: Some serine proteases, such as trypsin and chymotrypsin, are important digestive enzymes in the digestive system of mirid bugs. In order to better understand the role of serine proteases in the digestive system of the green plant bug, Apolygus lucorum (Meyer-Dür), we cloned the cDNA encoding serine protease of A. lucorum for the first time in the laboratory, which was named as AlSP4 (GenBank accession no. JQ609682). The results of sequence analysis showed that the open reading frame (ORF) of AlSP4 is 999 bp in length, encoding a 332-amino-acid peptide, with the predicted molecular weight (MW) of 36.84 kDa and the theoretical isoelectric point (pI) of 5.35, and the predicted N-terminal hydrophobic region containing 16 amino acid residues displays the typical feature of a signal peptide. Protein signature analysis revealed that the protein encoded by AlSP4 shares typical structural features of serine proteases with other insects, including His, Asp, and Ser residues for the catalytic amino acid triad of active sites of serine proteases. Putative trypsin precursors from the encoded protein of AlSP4 cDNA contain a signal peptide, activation peptide, and conserved N-termini (IVGG). By the Real-time PCR technique, we determined the expression pattern of AlSP4 in A. lucorum fed on different hosts. The expression level of AlSP4 was the highest in female adult A. lucorum fed on Bt cottons, significantly higher than that fed on conventional cotton (P＜0.01). The expression of AlSP4 increased significantly in male adult A. lucorum fed on Bt cottons, its expression level was only lower than that fed on garland chrysanthemum and significantly higher than that fed on conventional cottons (P＜0.01). Therefore, AlSP4 is the important digestive enzyme gene for adult A. lucorum to feed on Bt cottons, and plays an important role in adaption of A. lucorum to survive on Bt cottons.

Key words: Apolygus lucorum, serine protease, trypsin, expression pattern analysis, host plant