Effects of parental genetic divergence on gene expression patterns in interspecific hybrids of Camellia.

BACKGROUND: The merging of two divergent genomes during hybridization can result in the remodeling of parental gene expression in hybrids. A molecular basis underling expression change in hybrid is regulatory divergence, which may change with the parental genetic divergence. However, there still no unanimous conclusion for this hypothesis. RESULTS: Three species of Camellia with a range of genetic divergence and their F1 hybrids were used to study the effect of parental genetic divergence on gene expression and regulatory patterns in hybrids by RNA-sequencing and allelic expression analysis. We found that though the proportion of differentially expressed genes (DEGs) between the hybrids and their parents did not increase, a greater proportion of DEGs would be non-additively (especially transgressively) expressed in the hybrids as genomes between the parents become more divergent. In addition, the proportion of genes with significant evidence of cis-regulatory divergence increased, whereas with trans-regulatory divergence decreased with parental genetic divergence. CONCLUSIONS: The discordance within hybrid would intensify as the parents become more divergent, manifesting as more DEGs would be non-additively expressed. Trans-regulatory divergence contributed more to the additively inherited genes than cis, however, its contribution to expression difference would be weakened as cis mutations accumulated over time; and this might be an important reason for that the more divergent the parents are, the greater proportion of DEGs would be non-additively expressed in hybrid.

Transcriptome analysis reveals hybridization-induced genome shock in an interspecific F1 hybrid from Camellia.

The combination of two divergent genomes during hybridization can result in "genome shock". Although genome shock has been reported in the hybrids of some herbaceous plants, the pattern and the principle it follows are far from understood, especially in woody plants. Here, the gene expression patterns were remodeled in the F1 hybrid from the crossing of Camellia azalea × Camellia amplexicaulis compared with the parents as revealed by RNA-seq. About 54.5% of all unigenes were differentially expressed between the F1 hybrid and at least one of the parents, including 6404 unigenes with the highest expression level in the F1 hybrid. A series of genes, related to flower development, essential for RNA-directed DNA methylation and histone methylation, as well as 223 transposable elements, were enriched; and most of them exhibited a higher level of expression in the F1 hybrid. These results indicated that the genome shock induced by interspecific hybridization in Camellia could indeed result in changes of gene expression patterns, potentially through regulating DNA methylation and histone methylation which may be helpful for the maintaining of genome stability and even related to the unique phenotype of the F1 hybrid.