Transcriptome Analysis of Heterosis in Survival in the Hybrid Progenies of 'Haida No.1' and Orange-Shelled Lines of the Pacific Oyster Crassostrea gigas

Heterosis has been exploited to enhance the yield and adaptability in various shellfish species; however, the molecular basis of it remains unclear. The Pacific oyster Crassostrea gigas is one of the most economically important aquaculture species, and its productive traits can be improved by hybridization. Here, an intraspecific cross between orange shell(O, 10th generation) and ’Haida No. 1’(H, 13th generation) of C. gigas was performed to assess the heterosis of survival trait. Survival rates of hybrid family(OH) and inbred families(HH and OO) were compared at larval stage, and eyed-pediveliger larvae of three families were subjected to transcriptome analysis. The analysis results of best-parent heterosis and mid-parent heterosis showed that the hybrid family exhibited a high heterosis in survival relative to the parental families. The OH-M(OH vs. OO) and OH-P(OH vs. HH) had 425 and 512 differentially expressed genes(DEGs), respectively. Functional enrichment analysis of these DEGs revealed that the significantly enriched genes function in virion binding, C-type lectin receptor signaling pathway, cellular defense response and other immune-related processes, which involves perlucin-like protein, CD209 antigen-like protein, ZNFX1, caspase-3 and acan genes. These differentially expressed genes in OH-M and OH-P, together with the immune-related processes mentioned above may play an important role in the larval survival of C. gigas. In addition, three genes(CYP450, fucolectin and perlucin-like) are associated with the orange shell and low survival of maternal oyster OO. These findings provide support for the application of hybrid with superior survival and will facilitate the understanding of heterosis formation in the Pacific oyster.