Identification of a novel Carassius amphitetraploid clone and its transcriptomic responses to herpesvirus infection

A major threat to gibel carp aquaculture is an epizootic disease caused by C. auratus herpesvirus (CaHV). Therefore, breeding of disease resistant strain is one of significant needs for the industry. Polyploids often show enhanced tolerance to abiotic or biotic stress. However, the effects of WGD are complex and the underlying mechanisms remain elusive. In this study, we first synthesized a group of novel amphitetraploids via crossing the eggs of gynogenetic C. gibelio clone A+ with the trypsin-treated sperm of sexual C. cuvieri and then established three gynogenetic amphitetraploid clones with different transferrin phenotypes. They all showed intermediate resistance to CaHV in relative to their parents. Subsequently, we uncovered distinct transcriptomic response to CaHV infection in the one amphitetraploid clone (CaA4n-I) compared with their parents. Interestingly, the coexpression gene network analysis showed that amphitetraploid CaA4n-I and their paternal C. cuvieri adopted different anti-viral strategies via up-regulating the expression of positive factors or down-regulating the expression of negative factors in immune response respectively. Moreover, we revealed the complicated changes of expression patterns, including additivity, maternal expression level dominance, paternal expression level dominance, transgressive up-regulation, and transgressive down-regulation, in the amphitetraploid CaA4n-I. After CaHV infection, the proportions of maternal expression level dominance and transgressive up-regulation increased and more C. cuvieri-derived homeologous genes altered expression patterns in the amphitetraploid CaA4n-I. The current study not only produces a candidate strain for C. auratus aquaculture, but also provides a transcriptomic picture how a newly synthetic animal allopolyploid to response to virus infection.