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C-type lectins (CTLs) function as pattern recognition receptors (PRRs) and play an important role in the innate immunity of insects. To investigate the role of CTLs in the antifungal responses, we analyzed expression profiles of 36 CTLs of Helicoverpa armigera in the tissues (hemocytes, fat bodies, and midgut) after the infection by entomopathogenic fungus Metarhizium rileyi. The expression levels of many HaCTLs were found to be up-regulated after the infection. Four recombinant HaCTLs (rHaCTL11, rHaCTL12, rHaCTL27, and rHaCTL45) were expressed and purified. Analysis of the purified rHaCTLs revealed that rHaCTLs were able to bind to conidia and hyphal bodies of M. rileyi , and the affinity of rHaCTL11 and rHaCTL27 for hyphal bodies was weaker than for conidia. All these rHaCTLs agglutinate conidia and hyphal bodies in a calcium (Ca2+) dependent manner. Sugar specificity assays showed that d -trehalose, mannan, β-1,3-glucan, d -galactose, glucose, d -raffinose, lipopolysaccharide, and d -xylose can inhibit the binding of HaCTLs to M. rileyi. Additionally, survival assays showed that pretreatment of fungal conidia with rHaCTL11 significantly reduced the rate of host death, and knockdown of HaCTL11 significantly increased H. armigera sensitivity to fungal infection. These results suggest that HaCTLs play significant role as PRRs in the defense of H. armigera against M. rileyi infection. • Expression profiles of 36 CTLs of Helicoverpa armigera after the infection by fungi were analyzed. • rHaCTLs were able to bind to Metarhizium rileyi conidia and hyphal bodies. • rHaCTLs agglutinate conidia and hyphal bodies in a calcium dependent manner. • Some sugars can inhibit the binding of HaCTLs to M. rileyi. • HaCTLs play significant role as PRRs in the defense of H. armigera against M. rileyi infection. [ABSTRACT FROM AUTHOR]

In the immune system, C-type lectins, as pattern recognition receptors, have an important function. Carbohydrate-recognition domains (CRDs) endow C-type lectins with the function of recognizing and scavenging non-self factors. In the present study, a new C-type lectin (designated as PtCTL-9 according to the order of discovery) from swimming crab (Portunus trituberculatus) was characterized. QPN (Gln-Pro-Asn) and FHS (Phe-His-Ser) were identified as the key motifs that determine carbohydrate binding. Motif QPN was mutated to QPD (Gln-Pro-Asp) (M1) and EPN (Glu-Pro-Asn) (M2) to study its immune function and for comparative analysis. The results showed that PtCTL-9 displayed broad non-self immunity. PtCTL-9 could also function as an opsonin to promote phagocytosis and the in vitro encapsulation of hemocytes. These results indicated that PtCTL-9 has an extensive nonself-recognition ability, regulates pathogen clearance, and its QPN motif is important in PtCTL-9's immune function. • A C-type lectin PtCTL-9 with a novel QPN motif was identified from Portunus trituberculatus. • PtCTL-9 possessed strong binding activity to nonself particles while its two mutants displayed weak binding activity. • PtCTL-9 inhibited the growth of S. cerevisiae. • PtCTL-9 promoted phagocytosis and encapsulation activity of hemocytes in vitro. [ABSTRACT FROM AUTHOR]