The pan-plastome of tartary buckwheat (fagopyrum tataricum): key insights into genetic diversity and the history of lineage divergence

Abstract

Abstract Background Tartary buckwheat (Fagopyrum tataricum) is an important food and medicine crop plant, which has been cultivated for 4000 years. A nuclear genome has been generated for this species, while an intraspecific pan-plastome has yet to be produced. As such a detailed understanding of the maternal genealogy of Tartary buckwheat has not been thoroughly investigated. Results In this study, we de novo assembled 513 complete plastomes of Fagopyrum and compared with 8 complete plastomes of Fagopyrum downloaded from the NCBI database to construct a pan-plastome for F. tartaricum and resolve genomic variation. The complete plastomes of the 513 newly assembled Fagopyrum plastome sizes ranged from 159,253 bp to 159,576 bp with total GC contents ranged from 37.76 to 37.97%. These plastomes all maintained the typical quadripartite structure, consisting of a pair of inverted repeat regions (IRA and IRB) separated by a large single copy region (LSC) and a small single copy region (SSC). Although the structure and gene content of the Fagopyrum plastomes are conserved, numerous nucleotide variations were detected from which population structure could be resolved. The nucleotide variants were most abundant in the non-coding regions of the genome and of those the intergenic regions had the most. Mutational hotspots were primarily found in the LSC regions. The complete 521 Fagopyrum plastomes were divided into five genetic clusters, among which 509 Tartary buckwheat plastomes were divided into three genetic clusters (Ft-I/Ft-II/Ft-III). The genetic diversity in the Tartary buckwheat genetic clusters was the greatest in Ft-III, and the genetic distance between Ft-I and Ft-II was the largest. Based on the results of population structure and genetic diversity analysis, Ft-III was further subdivided into three subgroups Ft-IIIa, Ft-IIIb, and Ft-IIIc. Divergence time estimation indicated that the genera Fagopyrum and Rheum (rhubarb) shared a common ancestor about 48 million years ago (mya) and that intraspecies divergence in Tartary buckwheat began around 0.42 mya. Conclusions The resolution of pan-plastome diversity in Tartary buckwheat provides an important resource for future projects such as marker-assisted breeding and germplasm preservation.