Chitin synthase 1 gene and its two alternative splicing variants from two sap-sucking insects, Nilaparvata lugens and Laodelphax striatellus (Hemiptera: Delphacidae)

Abstract

Chitin synthase (CHS) is an enzyme that is required for chitin formation in insect cuticles and other tissues. In this study, CHS genes from two destructive rice insect pests, the brown planthopper Nilaparvata lugens and the small brown planthopper Laodelphax striatellus, were cloned. Phylogenetic analysis showed that these genes belonged to class CHS1 of the CHS gene family. Most insects possess two CHS genes (CHS1 and CHS2); however, genome and transcriptome searches showed that N. lugens possibly possess only CHS1 in both databases. Two transcript variants (CHS1a and CHS1b) resulting from exclusively alternative splicing (exon 19a or 19b in N. lugens) were identified for each of the two rice planthopper CHS1s. Gene structure comparison using the genomes that are currently sequenced showed that the CHS1 genes in all insects except Acyrthosiphon pisum have two transcript variants. Transcription of NlCHS1a reached its highest level just after molting, whereas NlCHS1b reached its highest expression level 1-2 days before molting. Injection of the N. lugens nymphs with double-strand RNA (dsRNA) of CHS1, CHS1a and CHS1b reduced the corresponding variant transcript levels and exhibited subsequent phenotypes. Silencing of CHS1 and CHS1a resulted in elongated distal wing pads and the "wasp-waisted" or crimpled cuticle phenotypes and eventually died, whereas the phenotypes caused by injection of NlCHS1b dsRNA seem not so obvious although slightly increased mortality was observed. Our results suggest that N. lugens likely lacks CHS2 and CHS1 may be efficient target gene for RNAi-based N. lugens control.