Chitin deacetylases (CDAs) are enzymes required for one of the pathways of chitin degradation, in which chitosan is produced by the deacetylation of chitin. Bioinformatic investigations with genomic and transcriptomic databases identified four genes encoding CDAs in Nilaparvata lugens (NlCDAs). Phylogenetic analysis showed that insect CDAs were clustered into five major groups. Group I, III and IV CDAs are found in all insect species, whereas the pupa-specific group II and gut-specific group V CDAs are not found in the plant-sap/blood-sucking hemimetabolous species from Hemiptera and Anoplura. The developmental and tissue-specific expression patterns of four NlCDAs revealed that NlCDA3 was a gut-specific CDA, with high expression at all developmental stages; NlCDA1, NlCDA2 and NlCDA4 were highly expressed in the integument and peaked periodically during every moulting, which suggests their roles in chitin turnover of the insect old cuticle. Lethal phenotypes of cuticle shedding failure and high mortality after the injection of double-stranded RNAs (dsRNAs) for NlCDA1, NlCDA2 and NlCDA4 provide further evidence for their functions associated with moulting. No observable morphological and internal structural abnormality was obtained in insects treated with dsRNA for gut-specific NlCDA3.

In insect eggs, the chorion has the essential function of protecting the embryo from external agents during development while allowing gas exchange for respiration. In this study, we found a novel gene, Nilaparvata lugens chorion protein (NlChP), that is involved in chorion formation in the brown planthopper, Nilaparvata lugens. NlChP was highly expressed in the follicular cells of female adult brown planthoppers. Knockdown of NlChP resulted in oocyte malformation and the inability to perform oviposition, and electron microscopy showed that the malformed oocytes had thin and rough endochorion layers compared to the control group. Liquid chromatography with tandem mass spectrometry analysis of the eggshell components revealed four unique peptides that were matched to NlChP. Our results demonstrate that NlChP is a novel chorion protein essential for egg maturation in N. lugens, a hemipteran insect with telotrophic meroistic ovaries. NlChP may be a potential target in RNA interference-based insect pest management.