Chitinases are important enzymes required for chitin degradation and reconstruction in insects. Based on a bioinformatics investigation, we identified 12 genes encoding putative chitinase-like proteins, including 10 chitinases (Cht), one imaginal disc growth factor (IDGF) and one endo-β-N-acetylglucosaminidase (ENGase) in the genome of the brown planthopper, Nilaparvata lugens (Hemiptera: Delphacidae). These 12 genes were clustered into nine different groups, with 11 in glycoside hydrolase family 18 groups (groups I-VIII) and one in the ENGase group. Developmental and tissue-specific expression pattern analysis revealed that the transcript levels of eight genes peaked periodically during moulting and were mainly expressed in the integument, except NlCht2, NlCht4, NlIDGF and NlENGase. NlCht2, NlIDGF and NlENGase were expressed at all stages with slight periodical changes and mainly expressed in the female reproductive organs in adults, whereas NlCht4 was highly expressed only at the adult stage in the male reproductive organs. Lethal phenotypes were observed in insects challenged by double-stranded RNAs for NlCht1, NlCht5, NlCht7, NlCht9 and NlCht10 during moulting, suggesting their significant roles in old cuticle degradation. NlCht1 was the most sensitive gene, inducing 50% mortality even at 0.01 ng per insect. Our results illustrate the structural and functional differences of chitinase-like family genes and provide potential targets for RNA interference-based rice planthopper management.

The brown planthopper (BPH), Nilaparvata lugens, is a major rice pest in Asia, and accumulated evidence indicates that this species is susceptible to RNA interference (RNAi); however, the mechanism underlying RNAi and parental RNAi has not yet been determined. We comprehensively investigated the repertoire of core genes involved in small interfering RNA (siRNA) and micro-RNA (miRNA) pathways in the BPH by comparing its newly assembled transcriptome and genome with those of Drosophila melanogaster, Tribolium castaneum and Caenorhabditis elegans. Our analysis showed that the BPH possesses one drosha and two Dicer (dcr) genes, three dsRNA-binding motif protein genes, two Argonaute (ago) genes, two Eri-1-like genes (eri-1), and a Sid-1-like gene (sid-1). Additionally, we report for first time that parental RNAi might occur in this species, and siRNA pathway and Sid-1 were required for high efficiency of systemic RNAi triggered by exogenous dsRNA. Furthermore, our results also demonstrated that the miRNA pathway was involved in BPH metamorphosis as depletion of the ago1 or dcr1 gene severely impaired ecdysis. The BPH might be a good model system to study the molecular mechanism of systemic RNAi in hemimetabolous insects, and RNAi has potential to be developed to control this pest in agricultural settings.

The coding regions for the major epitopes of structural protein VP2 (vp2e) and structural protein VP3 were amplified from marine birnavirus (MABV) cDNA and efficiently expressed as glutathione S-transferase (GST) fusion proteins in Escherichia coli. Polyclonal antibodies against VP2e and VP3 were raised in rabbits and fish using the purified proteins of GST/VP2e and GST/VP3. The rabbit anti-serum against VP3 was more sensitive than the rabbit anti-VP2e serum in detecting virus in MABV-infected fish, while fish anti-VP2e serum showed a stronger neutralization response than fish anti-VP3 serum.