Immune Functional Analysis of Chitin Deacetylase 3 from the Asian Citrus Psyllid Diaphorina citri

Chitin deacetylase (CDA) is a chitin degradation enzyme that strictly catalyzes the deacetylation of chitin to form chitosan, which plays an important role in regulating growth and development, as well as the immune response. In this study, a chitin deacetylase 3 gene (CDA3) was identified with a complete open reading frame (ORF) of 1362 bp from the genome database of Diaphorina citri, encoding a protein of 453 amino acids. Spatiotemporal expression analysis suggested that D. citri CDA3 (DcCDA3) had the highest expression level in the integument and third-instar nymph stage. Furthermore, DcCDA3 expression level can be induced by 20-hydroxyecdysone (20E). Injection of Escherichia coli and Staphylococcus aureus induced the upregulation of DcCDA3 in the midgut, while DcCDA3 was downregulated in the fat body. After silencing DcCDA3 by RNA interference, there was no influence on the D. citri phenotype. In addition, bactericidal tests showed that recombinant DcCDA3 inhibited gram-positive bacteria, including S. aureus and Bacillus subtilis (B. subtilis). In conclusion, our results suggest that DcCDA3 might play an important role in the immune response of D. citri.