Abstract
BackgroundHeterosis has been exploited for decades in different animals and crops due to it resulting in dramatic increases in yield and adaptability. Hybridization is a classical breeding method that can effectively improve the genetic characteristics of organisms through heterosis. Abalone has become an increasingly economically important aquaculture resource with high commercial value. However, due to changing climate, abalone is now facing serious threats of high temperature in summer. Interspecific hybrid abalone (Haliotis gigantea ♀ × H. discus hannai ♂, SD) has been cultured at large scale in southern China and has been shown high survival rates under heat stress in summer. Therefore, SD has become a good model material for heterosis research, but the molecular basis of heterosis remains elusive.ResultsHeterosis in thermal tolerance of SD was verified through Arrhenius break temperatures (ABT) of cardiac performance in this study. Then RNA-Sequencing was conducted to obtain gene expression patterns and alternative splicing events at control temperature (20 °C) and heat stress temperature (30 °C). A total of 356 (317 genes), 476 (435genes), and 876 (726 genes) significantly diverged alternative splicing events were identified in H. discus hannai (DD), H. gigantea (SS), and SD in response to heat stress, respectively. In the heat stress groups, 93.37% (20,512 of 21,969) of the expressed genes showed non-additive expression patterns, and over-dominance expression patterns of genes account for the highest proportion (40.15%). KEGG pathway enrichment analysis showed that the overlapping genes among common DEGs and NAGs were significantly enriched in protein processing in the endoplasmic reticulum, mitophagy, and NF-κB signaling pathway. In addition, we found that among these overlap genes, 39 genes had undergone alternative splicing events in SD. These pathways and genes may play an important role in the thermal resistance of hybrid abalone.ConclusionMore alternative splicing events and non-additive expressed genes were detected in hybrid under heat stress and this may contribute to its thermal heterosis. These results might provide clues as to how hybrid abalone has a better physiological regulation ability than its parents under heat stress, to increase our understanding of heterosis in abalone.
Highlights
Heterosis has been exploited for decades in different animals and crops due to it resulting in dramatic increases in yield and adaptability
The discussion of the genetic basis of heterosis has lasted for nearly a century, but that of the molecular mechanism of heterosis still remain elusive Next-generation sequencing (NGS) technologies offer the potential to uncover the molecular mechanism of heterosis at the transcriptional level [8]
Five alternative splicing (AS) events types have been recognized in animals, including skipped exons (SE), alternative 5’splice sites (A5SS), alternative 3’splice sites (A3SS), retained introns (RI), and mutually exclusive exons (MXE) [21]
Summary
Heterosis has been exploited for decades in different animals and crops due to it resulting in dramatic increases in yield and adaptability. A batch of hybrid livestock (e.g., pig) and crops (e.g., rice) have shown better performance in growth and environmental adaptation when compared with their parents, it has received extensive research [2]. Various genetic models have been put forward to explain heterosis, including dominance, overdominance, and epistatic hypothesis [3]. The overdominance hypothesis has been supported by a lot of experimental research [4,5,6], in which nonadditive effects are described as a consequence of genetic differences between the homozygous parents and their heterozygous hybrids [7]. Transcriptomic analysis provides an efficient way to explore heterosis, and its results mainly include abundant differential expressed genes and alternative splicing (AS) events. As a post-transcriptional regulation process modulating gene expression, AS has been reported to play an important role in heterosis establishment [22]
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