Transcriptome profiling of Penaeus vannamei hepatopancreas infected with WSSV following feeding diet containing ulvan

The present study aimed to elucidate the mechanism of protection provided by dietary ulvan as observed in previous studies. Thirty shrimps (3.35 ± 0.08 g average body weight) were stocked in six polyethylene tanks (5 shrimps tank-1, treatments were in three replicate/tank) and were fed either a diet containing no ulvan (control) or containing ulvan at 1 g kg diet-1 for 35 days at 10% body weight twice daily. At the termination of the feeding, the shrimps were subjected to a white spot syndrome virus (WSSV) challenge test via intramuscular injection of the viral inoculum. Shrimps were sacrificed after 24 h of exposure, and the hepatopancreas was excised for total RNA extraction for transcriptome profiling. Biological validation of the RNA-seq results was also performed for 10 immune-related genes (6 up- and 4 down-regulated genes). A comparison of the ulvan group with the control group revealed that 69 differentially expressed genes (DEGs) were significantly up-regulated, whereas 640 were significantly down-regulated. 184 DEGs between the control and ulvan-treated groups were classified into six KEGG categories of Metabolism (145 DEGs), Organismal systems (16), Human disease (4), Genetic Information Processing (10), Cellular Processes (2), and Environmental Information Processing (7). The 145 DEGs under Metabolism were distributed to Level 2 subcategories as carbohydrate metabolism (59 DEGs), global and overview maps (44), energy metabolism (27), and amino acid metabolism (15). All candidate immune-related genes (67) were down-regulated except for 5 genes. The validation experiment showed proportionality of gene expressions of the qPCR and of those in the assembled transcriptome, justifying the acceptability of the RNA-seq results. In conclusion, data from the present study provided mechanisms for protecting the white shrimp by dietary ulvan against WSSV infection.