Cloning and expression analysis of Chitinase-2 from Penaeus monodon during molting cycle and different larval developmental stages

We obtained the full-length cDNA sequence of PmChi (GenBank accession number:KX610684, namely PmChi-2) from black tiger shrimps (Penaeus monodon) by transcriptome sequencing and rapid amplification of cDNA ends (RACE). The full length of PmChi-2 cDNA was 2 050 bp, including a 1 587 bp ORF (open reading frame) which encoded 528 amino acid residues, a 144 bp 5′-UTR and a 319 bp 3′-UTR. Phylogenetic analyses suggest that the predicted amino acid sequence of PmChi-2 shared 78%~97% identity with the type of Chi-2 of other crustaceans. Relative gene expression levels of PmChi-2 gene in various tissues were then detected by qRT-PCR (quantitative real-time PCR) during the molting cycle and different larval developmental stages. The results show that PmChi-2 had the highest gene expression level in cuticle in the premolt, then decreased in a descending order (stomach > gill > thoracic ganglia > eyestalk), while weak expression was detected in the other tissues. The gene expression patterns of PmChi-2 were different among tissues during the molting cycle. PmChi-2 mRNA had the highest expression level at Stage A and the lowest expression level at Stage E in gill. PmChi-2 mRNA had the highest expression level at Stage D and the lowest expression level at Stage E in stomach. PmChi-2 mRNA had the highest expression level at Stage D and the lowest expression level at Stage E in cuticle, which suggests that PmChi-2 may participate in the molting. At different larval developmental stages,  PmChi-2 mRNA had the highest expression level at Mysis 3, indicating that PmChi-2 was associated with larval metamorphosis. The results lay a foundation for research on the biological function and regulation of chitinase in P.monodon.