Global transcriptional and miRNA insights into bases of heterosis in hybridization of Cyprinidae

Hybrid Megalobrama amblycephala x Culter alburnus represents a population newly formed by interspecific crossing between two different genera. Here we assessed the expression pattern of mRNA and small RNA in newly formed F-1, F-2 and their progenitors. Large amounts of nonadditively expressed protein-coding genes showed parental expression level dominance (ELD). Interestingly, the ELD pattern could inherit from F-1 to F-2, which guaranteed a stable appearance in progenies. The ELD-B genes were found to contribute to cell development, while the ELD-T genes were enriched in function of stress and adaptability. microRNAs (miRNA) also had similar expression patterns to genes. A high proportion of miRNAs showed nonadditive expression upon hybridization, and were found to target important genes with diverse roles potentially involved in stress adaption and development. Taken together, the gene and miRNA expression divergence contributes to heterosis in the newly formed hybrid, promising the successful existence of hybrid speciation.