Abstract: 【Aim】 To identify the expression patterns of caspase in Spodoptera exigua induced by apoptosis inducer and under pathogenic microorganism stress, so as to lay a foundation for further study on the mechanism of apoptosis in Lepidoptera insects. 【Methods】 RT-PCR was used to amplify the full-length coding regions of two caspase genes (SeCasp-3 and SeCasp-4) from the 3rd instar larvae of S. exigua. qPCR was used to detect the expression patterns of the two SeCasp genes in the fat body cells of S. exigua after induction by apoptosis inducers hydrogen peroxide (H₂O₂) (100 μmol/L), actinomycin D (ActD) (10 μg/mL) and dexamethasone (DEX) (50 μg/mL), and in the 3rd instar larvae of S. exigua infected by pathogens Bacillus thuringiensis kurstaki (10⁸ colonies/mL), Escherichia coli TG1 (10⁸ colonies/mL), Heliothis virescens ascovirus 3h (HvAV-3h) (1.16×10¹¹genome copies/mL) and Autographa californica multiple nucleopolyhedrovirus (AcMNPV) (5 000 OBs/μL). 【Results】 The coding regions of SeCasp-3 (GenBank accession no.: MW183334) and SeCasp-4 (GenBank accession no.: MW183335) are 942 and 843 bp in length, encoding 313 and 280 amino acids, respectively. The putative protein sequences of SeCasp-3 and SeCasp-4 show 45.54% and 58.46% amino acid sequence identities with Dronc of Bombyx mori, respectively, and SeCasp-3 and SeCasp-4 show high homology. SeCasp-3 and SeCasp-4 exhibited different expression patterns in the fat body cells of S. exigua induced by different chemicals. The relative expression levels of both SeCasp-3 and SeCasp-4 in the fat body cells treated by 100 μmol/L H₂O₂ and 10 μg/mL ActD for 24 and 48 h were significantly up-regulated. In the fat body cells of S. exigua treated by 50 μg/mL DEX for 24 and 48 h, the relative expression level of SeCasp-3 showed no significant change, but that of SeCasp-4 was significantly enhanced by several thousand folds as compared to the control. The expression patterns of SeCasp-3 and SeCasp-4 in the 3rd instar larvae of S. exigua infected by different pathogens were basically similar. The general linear model analysis showed that the infection of B. thuringiensis kurstaki and E. coli TG1 caused no significant change in the expression levels of SeCasp-3 and SeCasp-4 in the 3rd instar larvae of S. exigua, while the infection of HvAV-3h and AcMNPV significantly inhibited the expression of the two genes. 【Conclusion】 Two S. exigua caspase genes were identified and their expression responses to apoptosis inducers and pathogenic microorganism infection were assayed in this study, laying a foundation for further exploring the function of caspase and process of insect apoptosis.

Key words: Spodoptera exigua, apoptosis, pathogens, caspase, SeCasp, Dronc