Characterization of hemocyanin-like subunits in giant freshwater prawn Macrobrachium rosenbergii.

Macrobrachium rosenbergii, a freshwater prawn, is one of the leading cultured and exported species of prawn in the world. Disease outbreaks such as the White Spot Syndrome Virus (WSSV) led to the decline of shrimp production. Shrimps and prawns only rely in the innate immune system against viruses and there is little knowledge about the genome of M. rosenbergii. Contig 13 (C13) and Contig 37 (C37), originally found in the genome of Marsupenaeus japonicus and of unknown identity and function, were predicted to be homologous to corresponding WSSV ORFs suggesting interactions between the virus and its host. The study aims to confirm the presence of C13 and C37 in M. rosenbergii and characterize the two contigs in the prawn. Through Rapid amplification of cDNA ends-Polymerase Chain Reaction (RACE–PCR), 1,256 bp for C13 and 1,118 bp for C37 were obtained from the sequences. Both contigs are predicted to be a hemocyanin gene and has a role in the innate host defense in shrimps and prawns. Basic Local Alignment Search Tool (BLAST) coupled with homologous sequences in NCBI-GenBank revealed the homology of each contig to hemocyanin. Multiple sequence alignment revealed several conserved regions of C13 and C37 with other hemocyanin of shrimp and prawn species. Interestingly, a maximum parsimony tree created a clade with C13 grouping with freshwater shrimp species, closely related to Macrobrachium nipponense with 81% bootstrap support; and C37 with saltwater shrimp species with a bootstrap support of 95%. Gene expression revealed that C37 is found to be expressed in the heart, hepatopancreas, muscle, intestine, hemocyte, and pleopods of healthy M. rosenbergii while the gene is found to be upregulated at the early stages of its WSSV infection.