Evolutionary patterns of plastome resolve multiple origins of the Ns-containing polyploid species in Triticeae

Tracing evolutionary history proves challenging for polyploid groups that have evolved rapidly, especially if an ancestor of a polyploid is extinct. TheNs-containing polyploids are recognized as theNsXmandStHNsXmgenomic constitutions in Triticeae. TheNsoriginated fromPsathyrostachys, while theXmrepresented a genome of unknown origin. Here, we use genetic information in plastome to trace the complex lineage history of theNs-containing polyploid species by sampling 26 polyploids and 90 diploid taxa representing 23 basic genomes in Triticeae. Phylogenetic reconstruction, cluster plot of genetic distance matrix, and migration event demonstrated that (1) theNsplastome originated from differentPsathyrostachysspecies, and theXmplastome may originate from an ancestral lineage ofHenrardia,Agropyron, andEremopyrum; (2) theNs,Xm, andStgenome donors separately served as the maternal parents during the speciation of theNs-containing polyploid species, resulting in a maternal haplotype polymorphism; (3) North AmericanLeymusspecies might originate from colonization during late Miocene via the Bering land bridge and were the paternal donor of theStHNsXmgenomePascopyrumspecies. Our results shed new light on our understanding of the rich diversity and ecological adaptation of theNs-containing polyploid species.