In plant evolutionary history, various factors including convergent evolution, incomplete lineage sorting, hybridization and introgression, may cause phylogenetic incongruence between nuclear and plastid DNA. One extreme result of hybridization is plastid capture, in which the cytoplasm of one species is replaced by that of another species through inter-species hybridization and subsequent backcrossing, yielding a plant with a novel combination of nuclear and plastid genomes.
Saxifragaceae, a family of over 600 species and approximately 30 genera of herbaceous perennials, are found mostly in the Northern Hemisphere with centers of diversity in the Himalayas, East Asia and Western North America. The family comprises two main lineages: Saxifragoids, which include Saxifraga and Saxifragella and Heucheroids, which include all other genera. The Heucheroids are noted for examples of intergeneric hybridization. For example, nine genera of herbaceous perennials comprise the Heuchera group, a particularly valuable model for the analysis of plastid capture and its impact on phylogeny reconstruction due to evidence of numerous hybridization events among and within those genera.
In this study, we investigated plastome evolution across the family, reconstructed the phylogeny of the Heuchera group and examined putative plastid capture between Heuchera and Tiarella. Seven species representing Tiarella, as well as Mitella and Heuchera, were selected for genome skimming. Using nuclear ITS+ETS and the complete plastome, we fully resolved the species relationships of Tiarella, finding that the genus is monophyletic and the Asian species is most closely related to the western North American species. However, the position of Heuchera species was highly incongruent between nuclear and plastid data. Comparisons of nuclear and plastid phylogenies revealed that multiple plastid capture events have occurred between Heuchera and Tiarella, through putative ancient hybridization.
This study published online on April 28, 2020, including “Plastome evolution in Saxifragaceae and multiple plastid capture events involving Heuchera and Tiarella” and was published in Frontiers in Plant Science (SCI AREA II, IF3 years =4.025). Dr. Luxian Liu is the first author of this study, Prof. Fude Shang and Associate Prof. Pan Li of Zhejiang University are the corresponding authors. Moreover, Prof. Douglas E. Soltis of University of Florida and his postdoctoral fellow Ryan A. Folk are also involved in part of the research work. This study was supported by the National Natural Science Foundation of China (NOs.31900188).
Paper link：https://www.frontiersin.org/articles/10.3389/fpls.2020.00361/full.
DOI: 10.3389/fpls.2020.00361
