Functionality of highly diverged Imd like genes identified in stinkbugs and bedbugs.

The IMD pathway is an innate immune signalling pathway regulating antibacterial humoral defence responses, and is highly conserved among diverse insects and other organisms. However, genomic studies among hemipterans suggested that certain insects from this order may lack the Imd gene, a key component of the IMD immune pathway. Our previous work identified Imd in the brown-winged green stinkbug Plautia stali, which showed low sequence homology to other insect Imd genes but exhibited functionality in the IMD pathway. Using the P. stali Imd sequence as a query, we surveyed genomic data of the common bedbug Cimex lectularius and the brown marmorated stinkbug Halyomorpha halys, both of which were thought to lack an Imd gene, and identified Imd-like gene sequences in each. RNA interference experiments demonstrated that, in both species, these Imd-like genes function similarly to the canonical Imd gene. 3D protein structure predictions confirmed that, despite extensive sequence divergence, the Imd-like translation products were structurally similar to Imd proteins of other organisms. High levels of sequence diversity and positive selection were observed with some Imd-like genes of bedbugs and stinkbugs, suggesting an ongoing evolutionary arms race between insect hosts and their microbial symbionts.