Genetic Structure And Evolutionary History Of The Genus Rehmannia

Rehmannia Libosch. ex Fisch. et Mey. belongs to Scrophulariaceae, including six species:R. glutinosa, R. chingii, R. solanifolia, R. piasezkii, R. elata and R. henryi. So far, most of the researches have focused on the medicinal composition and efficacy of R. glutinosa, a traditional Chinese medicine. Few studies are related to the population structure and evolutionary history about Rehmannia species. With the decrease of sequencing cost and the development of bioinformatics technology, the feasibility of developing single-copy nuclear gene markers in non-model plants has increased. In this study, to develop single-copy nuclear gene markers for the Rehmannia species, we blasted the transcriptome data of R. glutinosa with single-copy or low-copy nuclear genes that have been identified in plants. We collected 217 individuals of 22 populations from six Rehmannia species in their natural distribution area to investigate the genetic structure and interspecific phylogenetic relationships in this genus. The main analysis results are as follows:(1) 11153 sequences have chosen from R. glutinosa transcriptome data for BLAST.258 candidate sequences were screened to design primers. And 11 single-copy nuclear markers have been developed to elucidate the genetic structure and population history in Rehmannia species.(2) Since there is no variation between R. glutinosa and R. solanifolia, R. piasezkii and R. elata, they are considered as two separate species, respectively. Rehmannia species exhibited lower nuclear diversity. Compared with other species of the genus, the nuclear diversity of R. piasezkii is relatively higher. Most of nuclear loci are neutral. Meanwhile the values of Tajima's D and Fu & Li's F* were positive at a significant level (P<0.05) in some loci, suggested that populations might have experienced the bottleneck effect. Further examination found that all 11nuclear loci were not affected by the selection.(3) There is significant genetic differentiation among the species of Rehmannia. Interspecific genetic variation possessed a larger proportion than genetic variation within species. Structure analysis indicated that the best clustering result was K=3, which was consistent with the topology of phylogenetic tree. R. piasezkii was the basal taxon of the genus and R. glutinosa was sister to R. chingii and R. henryi.(4) The divergence time between Rehmannia and Triaenophora occurred approximately in the late Tertiary and early Quaternary. The differentiation time among species within the genus occurred in the late Pleistocene, and the speciation model showed a recent rapid radial differentiation of the genus. The geological events and the climate changes in the Pleistocene have had a considerable impact on the distribution and evolution of Rehmannia.