Identification, mRNA expression, and functional analysis of chitin synthase 1 gene and its two alternative splicing variants in oriental fruit fly, Bactrocera dorsalis

Alternative splicing contributes to the coordinated regulation of ferritin subunit levels in Bactrocera dorsalis (Hendel)

A constant ratio of ferritin heavy chain homolog (HCH) and light chain homolog (LCH) subunits seems to be required to compose the ferritin heteropolymer protein in insects. However, the mechanism by which insect LCH genes regulate protein levels remains unclear. We report that alternative promoters and alternative splicing contribute to maintaining a constant ratio of the two subunits, BdFer1HCH and BdFer2LCH (ferritin 1 HCH and ferritin 2 LCH), in Bactrocera dorsalis, a notorious quarantine pest. The genes BdFer1HCH and BdFer2LCH were identified with a series of potential transcription factor binding sites and were shown to be clustered within the genome in a "head to head" fashion. Thus, we unearthed a potential post-transcriptional mechanism to regulate the levels of LCH subunits, and confirmed that the expressions of BdFer1HCH and BdFer2LCH were induced by 20-hydroecdysone, iron overload, and immune challenge.

Exposure to diflubenzuron results in an up-regulation of a chitin synthase 1 gene in citrus red mite, Panonychus citri (Acari: Tetranychidae)

Chitin synthase synthesizes chitin, which is critical for the arthropod exoskeleton. In this study, we cloned the cDNA sequences of a chitin synthase 1 gene, PcCHS1, in the citrus red mite, Panonychus citri (McGregor), which is one of the most economically important pests of citrus worldwide. The full-length cDNA of PcCHS1 contains an open reading frame of 4605 bp of nucleotides, which encodes a protein of 1535 amino acid residues with a predicted molecular mass of 175.0 kDa. A phylogenetic analysis showed that PcCHS1 was most closely related to CHS1 from Tetranychus urticae. During P. citri development, PcCHS1 was constantly expressed in all stages but highly expressed in the egg stage (114.8-fold higher than in the adult). When larvae were exposed to diflubenzuron (DFB) for 6 h, the mite had a significantly high mortality rate, and the mRNA expression levels of PcCHS1 were significantly enhanced. These results indicate a promising use of DFB to control P. citri, by possibly acting as an inhibitor in chitin synthesis as indicated by the up-regulation of PcCHS1 after exposure to DFB.

Transcriptional regulation of a chitinase gene by 20-hydroxyecdysone and starvation in the oriental fruit fly, Bactrocera dorsalis

Insect chitinases are hydrolytic enzymes that are required for the degradation of glycosidic bonds of chitin. In this study, we identified and characterized a full-length cDNA of the chitinase gene (BdCht2) in the oriental fruit fly, Bactrocera dorsalis. The cDNA contains an open reading frame (ORF) of 1449 bp that encodes 483 amino acid residues and 126- and 296-bp non-coding regions at the 5'- and 3'-ends, respectively. The BdCht2 genome has four exons and three introns. The predicted molecular mass of the deduced BdCht2 is approximately 54.3 kDa, with an isoelectric point of 5.97. The 977 bp 5' flanking region was identified and the transcription factor binding sites were predicted. Bioinformatic analyses showed that the deduced amino acid sequence of BdCht2 had 34%-66% identity to that of chitinases identified in other insect species. Quantitative real-time PCR (qPCR) analyses indicated that BdCht2 was mainly expressed during the larval-pupal and pupal-adult transitions. The tissue-specific expression showed that the highest expression was in the integument, followed by the fat body and other tissues. Moreover, the expression of BdCht2 was upregulated significantly upon 20-hydroxyecdysone (20E) at different dose injections after 8 h compared to that of the control. Starvation also increased the expression of BdCht2 in the third-instar larvae and was suppressed again by re-feeding the insects. These results suggest that BdCht2 plays an important role in the molting process of B. dorsalis larvae and can be regulated by 20E.

Molecular cloning, characterization and mRNA expression of a chitin synthase 2 gene from the oriental fruit fly, Bactrocera dorsalis (Diptera: Tephritidae)

Chitin synthase (CHS), a potential target for eco-friendly insecticides, plays an essential role in chitin formation in insects. In this study, a full-length cDNA encoding chitin synthase 2 (BdCHS2) was cloned and characterized in the oriental fruit fly, Bactrocera dorsalis. The BdCHS2 cDNA had 4417 nucleotides, containing an open reading frame of 4122 nucleotides, which encoded 1373 amino acid residues with a predicted molecular weight of 158.5 kDa. Phylogenetic analysis with other insect CHSs suggested that BdCHS2 belongs to insect CHS2. The BdCHS2 transcript was predominately found in midgut but was detected at low levels in fat body, Malpighian tubules, integument, and trachea. Moreover, BdCHS2 was expressed in all developmental stages, and highly expressed in the feeding stages. There was a positive relationship between BdCHS2 expression and total chitin content during development. Furthermore, both the gene expression and chitin content in midgut decreased when the insect was fed for 24 h, then starved for 24 h, while they increased dramatically and rapidly under the condition of starvation for 24 h then feeding for 24 h. These results suggest that BdCHS2 may play an important role in regulating chitin content of the midgut, and subsequently affect the growth and development of B. dorsalis.