Functional Analysis of a CTL-X-Type Lectin CTL16 in Development and Innate Immunity of .

C-type lectins (CTLs) are a class of proteins containing carbohydrate recognition domains (CRDs), which are characteristic modules that recognize various glycoconjugates and function primarily in immunity. CTLs have been reported to affect growth and development and positively regulate innate immunity in . However, the regulatory mechanisms of TcCTL16 proteins are still unclear. Here, spatiotemporal analyses displayed that was highly expressed in late pupae and early adults. RNA interference in early larvae shortened their body length and narrowed their body width, leading to the death of 98% of the larvae in the pupal stage. Further analysis found that the expression level of muscle-regulation-related genes, including , , , , and , and muscle-composition-related genes, including and , were obviously down-regulated after silencing in . In addition, the transcription of was mainly distributed in the hemolymph. was significantly upregulated after challenges with lipopolysaccharides, peptidoglycans, , and . Recombinant CRDs of TcCTL16 bind directly to the tested bacteria (except ); they also induce extensive bacterial agglutination in the presence of Ca. On the contrary, after silencing in the late larval stage, were able to develop normally. Moreover, the transcript levels of seven antimicrobial peptide genes (, , , , , , and ) and one transcription factor gene () were significantly increased under challenge and led to an increased survival rate of when infected with or , suggesting that TcCTL16 deficiency could be compensated for by increasing AMP expression via the IMD pathways in . In conclusion, this study found that TcCTL16 could be involved in developmental regulation in early larvae and compensate for the loss of CTL function by regulating the expression of AMPs in late larvae, thus laying a solid foundation for further studies on CTLs.