Transcriptome shock in interspecific F-1 allotriploid hybrids between Brassica species

Interspecific hybridization drives the evolution of angiosperms and can be used to introduce novel alleles for important traits or to activate heterosis in crop breeding. Hybridization brings together gene expression networks from two different species, potentially causing global alterations of gene expression in the F-1 plants which is called 'transcriptome shock'. Here, we explored such a transcriptome shock in allotriploid Brassica hybrids. We generated interspecific F-1 allotriploid hybrids between the allotetraploid species Brassica napus and three accessions of the diploid species Brassica rapa. RNA-seq of the F-1 hybrids and the parental plants revealed that 26.34-30.89% of genes were differentially expressed between the parents. We also analyzed expression level dominance and homoeolog expression bias between the parents and the F-1 hybrids. The expression-level dominance biases of the A(r), A(n), and C-n subgenomes was genotype and stage dependent, whereas significant homoeolog expression bias was observed among three subgenomes from different parents. Furthermore, more genes were involved in trans regulation than in cis regulation in allotriploid F-1 hybrids. Our findings provide new insights into the transcriptomic responses of cross-species hybrids and hybrids showing heterosis, as well as a new method for promoting the breeding of desirable traits in polyploid Brassica species. This study characterizes transcriptome shock which is driven by interspecific hybridization, resulting in global alterations of gene expression in F(1)plants and activating heterosis in crop breeding.