Epigenetic modification brings new opportunities for gene capture by transposable elements in allopolyploid Brassica napus

Abstract

Polyploids are widespread in plants and are important drivers for evolution and biodiversity. Allopolyploidy activates transposable elements (TEs) and causes genomic shock. Plant genomes can regulate gene expression by changing the epigenetic modification of TEs, but the mechanism for TEs to capture genes remains to be explored. Helitron TEs used the “peel-and-paste” mechanism to achieve gene capture. We identified 3,156 capture events and 326 donor genes of Helitron TEs in Brassica napus (AnAnCnCn). The donor genes captured by TEs were related to the number, length and location of their exons. The gene-capturing TEs carrying donor gene fragments were evenly distributed on the genome, and more than half of them were involved in the construction of pseudogenes, becoming the reserve force for polyploid evolution. Gene fragment copies enhanced information storage, providing opportunities for gene mutation and the formation of new genes. Simultaneously, the siRNAs targeting TEs may act on the donor genes due to siRNA crosstalk, and the gene methylation levels increased and the expression levels decreased. The genome sought a balance between sacrificing donor gene expression and silencing TEs, allowing TEs to hide in the genome. In addition, epigenetic modifications may temporarily relax the control of gene capture during allopolyploidization. Our study identified and characterized gene capture events in B. napus, analyzed the effects of DNA methylation and siRNA on gene capture events, and explored the regulation mechanism of gene expression by TEs epigenetic modification during allopolyploidization, which will contribute to understanding the formation and evolution mechanism of allopolyploidy.