Abstract
BackgroundInterspecies hybridization is widely used to achieve heterosis or hybrid vigor, which has been observed and harnessed by breeders for centuries. Natural allopolyploid hybrids generally exhibit more superior heterosis than both the diploid progenies and their parental species. However, polyploid formation processes have been long ignored, the genetic basis of heterosis in polyploids remains elusive.ResultsIn the present study, triploid hybrids had been demonstrated to contain two sets of chromosomes from mother species and one set from father species. Cellular polyploidization process in the embryos had been traced. The triploid hybrids might be formed by failure formation of the second polarized genome during the second meiosis stage. Four spindle centers were observed in anaphase stage of the first cell division. Three spindle centers were observed in side of cell plate after the first cell division.The 5S rDNA genes of four types of groupers were cloned and analyzed. The diploid and triploid hybrids had been proved to contain the tandem chimera structures which were recombined by maternal and paternal monomer units. The results indicated that genome re-fusion had occurred in the hybrid progenies.To further elucidate the genetic patterns of diploid and triploid hybrids, fluorescence chromosome location had been carried out, maternal 5S gene (M-386) were used as the probe. The triploid hybrids contained fewer fluorescence loci numbers than the maternal species. The results indicated that participation of paternal 5S gene in the triploid hybrid genome had degraded the match rates of M-386 probe.ConclusionsOur study is the first to investigate the cellular formation processes of natural allopolyploids in hybrid fish, the cellular polyploidization process may be caused by failure formation of the second polarized genome during the meiosis, and our results will provide the molecular basis of hybrid vigor in interspecies hybridization.Electronic supplementary materialThe online version of this article (doi:10.1186/s12863-016-0443-9) contains supplementary material, which is available to authorized users.
Highlights
Interspecies hybridization is widely used to achieve heterosis or hybrid vigor, which has been observed and harnessed by breeders for centuries
The inheritance relationships of ‘st’ chromosome were displayed in Fig. 1-e; ‘st’ numbers of the groupers were 0, 6, 3, and 3 for E. coioides, E. lanceolatus, diploid hybrids, and triploid hybrids, respectively
The 781 bp sequences were the combination structure of 386 bp and 395 bp, the 790 bp sequences were the combination structure of 386 bp and 404 bp. These results indicated that the new sequences in the hybrids were combined with maternal and paternal monomeric sequences, the tandemly repeated units of the parental 5S ribosomal DNA (5S rDNA) genes might exchange with each other during the hybridization
Summary
Interspecies hybridization is widely used to achieve heterosis or hybrid vigor, which has been observed and harnessed by breeders for centuries. Natural allopolyploid hybrids generally exhibit more superior heterosis than both the diploid progenies and their parental species. Interspecies hybridization is a useful and important strategy for generating progeny with heterosis or hybrid vigor, which is a phenomenon that has been observed by naturalists, harnessed by breeders for centuries [1]. Hybrid polyploids have been found in many types of fish and have achieved great heterosis, such as hybrids of Carassius auratus red var. × Megalobrama amblycephala [5, 7, 8], Carassius auratus red var. Superior performance of polyploid hybrids has been detected and the related breeding methods have been frequently applied, the genetic basis of heterosis or hybrid vigor is still unclear [1, 11].
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