Identification and functional analysis of C-type lectin-domain proteins in Ostrinia furnacalis

C-type lectins (CTLs) are a large family of proteins characterized by a conserved carbohydrate-recognition domain (CRD) that recognize and bind various sugar ligands. Currently, the CTLs in agricultural pest populations remain largely unexplored. In this study, 29 CTLDP (CTL-domain protein) genes were identified in the Ostrinia furnacalis, a worldwide agricultural pest, including 10 CTL-S (Single-CRD), 14 IMLs (Dual-CRD) and 5 CTL-X (CRD with other domains). The comparative and structural analysis of CRD sequences reveals that these domains exhibit similarity in sequences and tertiary and diversity in carbohydrate recognition motifs. CTL-Ss and CTL-Xs are predominantly expressed in the epidermis of O. furnacalis, whereas IMLs are primarily expressed in the fat body and hemocytes, which are key tissues involved in cellular immunity in insects. Moreover, the expression of OfIMLs in response to diverse pathogenic microorganisms varies across different time points following immune challenge. Notably, this study provides the first evidence that six OfIMLs are involved in hemocytic encapsulation against Macrocentrus cingulum larvae transplanted into naive O. furnacalis larvae. Considering the significant roles of IMLs, we further identified CTLs from 16 insect and one crustacean species using genomic data from public databases. IML was present in only 12 species, while CTL-S and CTL-X were found in all 17 species. According to the phylogenetic analysis and chromosomal distribution patterns, we hypothesize that IMLs have evolved independently within different taxonomic groups via gene duplication. These results offer insights into further exploration of CTL functions in agricultural pest insects.