Differential expression of immune genes between two closely related beetle species with different immunocompetence following attack by Asecodes parviclava.

Yang X, Fors L, Slotte T, Theopold U, Binzer-Panchal M, Wheat CW, Hambäck PA


Endoparasitoid wasps are important natural enemies of many insect species and are major selective forces on the host immune system. Despite increased interest in insect anti-parasitoid immunity, there is sparse information on the evolutionary dynamics of biological pathways and gene regulation involved in host immune defence outside Drosophila species. We de novo assembled transcriptomes from two beetle species and used time-course differential expression analysis to investigate gene expression differences in closely related species Galerucella pusilla and G. calmariensis that are, respectively, resistant and susceptible against parasitoid infection by Asecodes parviclava parasitoids. Approximately 271 million and 224 million paired-ended reads were assembled and filtered to form 52,563 and 59,781 transcripts for G. pusilla and G. calmariensis respectively. In the whole transcriptome level, an enrichment of functional categories related to energy production, biosynthetic process and metabolic process were exhibited in both species. The main difference between species appear to be immune response and wound healing process mounted by G. pusilla larvae. Using reciprocal BLAST against the D. melanogaster proteome, 120 and 121 immune-related genes were identified in G. pusilla and G. calmariensis, respectively. More immune genes were differentially expressed in G. pusilla than in G. calmariensis, in particular genes involved in signalling, hematopoiesis and melanization. In contrast, only one gene was differentially expressed in G. calmariensis. Our study characterizes important genes and pathways involved in different immune functions after parasitoid infection, and supports the role of signalling and hematopoiesis genes as key players in host immunity in Galerucella against parasitoid wasps.