Evolutionary insight into the invasive allopolyploidy Spartina anglica inferred from multiple chloroplast DNA and nuclear Waxy gene

Abstract

Polyploidy has played an important role in the Spartina system. However, the genomic changes following polyploidy evolution are complex and poorly understood, especially in the recent allopolyploid species Spartina anglica. In the present study, we used the nuclear Waxy gene in conjunction with multiple chloroplast DNA genes (trnK intron + matK, rps16-trnK, rps16 intron, trnV-ndhC, trnT-trnL, ndhF, ccsA, and ycf3) to investigate the evolution of Waxy homoeologs and chloroplast genes following allopolyploid formation in S. anglica. Our results revealed that most of the chloroplast regions analyzed were conserved and undistinguishable from the maternal parent (Spartina alterniflora); however, some regions (trnK intron + matK and rps16-trnK) have already undergone some changes and are slightly differentiated from the maternal parent. In the nuclear Waxy gene, at least four copies were expected in S. anglica; however, only two homoeologous copies of maternal origin were recovered, which are evolving under selective constraints. Our results indicate that, despite the presumed genetic uniformity of S. anglica, some structural genome changes have occurred in Korean individuals, and thus, the S. anglica genome may be more dynamic than previously thought. This provides more insights into the evolutionary history of Spartina species and may have implications for the success and diversification of S. anglica.