Genetic Diversity of Oxytropis Species from the Center of the Genus Origin: Insight from Molecular Studies

The genus Oxytropis (Fabaceae) was formed from the ancient species of Astragalus presumably approximately 5.6 Ma ago in Southern Siberia. Our study summarized data on the genetic diversity of 69 populations of 31 Oxytropis species in the center of origin of the genus based on the sequencing of plastid genome markers. Most of the populations (82.6%) are characterized by high gene diversity (0.600–1.000), which indicates a relatively stable state. Phylogenetic relationships between most Oxytropis species remain unresolved. Three genetic complexes and four phyletic lineages have been identified. Some species form weakly differentiated complexes, which is probably caused by their relatively recent divergence and the demography processes, as well as interspecific hybridization and polyploidy characteristic of Oxytropis species.

Extensive Sampling Provides New Insights into Phylogenetic Relationships between Wild and Domesticated Zanthoxylum Species in China

Zanthoxylum, belonging to the Rutaceae family, is widely distributed in tropical and subtropical regions. The genus has high economic value as spices, oils, medicinal plants, and culinary applications. Zanthoxylum has a long history of domestication and cultivation in China. However, the phylogenetic relationships and origin of wild and cultivated Zanthoxylum species in China remain largely unknown. Moreover, there is still no clear molecular phylogenetic system for Zanthoxylum species. Herein, 373 Zanthoxylum samples were collected from all presently known provenances of Zanthoxylum in China. In this study, four chloroplast DNA (cpDNA) markers (matK, ndhH, psbB, rbcL) were used to comprehensively analyze the genetic diversity, relatedness, and geographical origin of Chinese Zanthoxylum species. The results were as follows: (1) The aligned length of the four pairs of cpDNA sequences was 3836 bp, and 68 haplotypes were identified according to 219 variable polymorphic sites, including 3 Indels (insertions and deletions), 129 parsimony informative sites, 90 singleton variable sites. (2) Phylogenetic tree and haplotype network strongly supported the division of Zanthoxylum species consistent with the taxonomic recognition of five species: Z. bungeanum, Z. piasezkii, Z. piperitum, Z. armatum, and Z. micranthum. (3) Divergence time estimation suggested that Zanthoxylum genus originated from the Late Eocene, and most Zanthoxylum species diverged after the Middle Miocene. (4) Haplotype 16 (H16) was at the bottom of the phylogenetic tree, had higher haplotype diversity (Hd) and nucleotide polymorphism (Pi) than other haplotypes, and was located in the center of the network figure. Therefore, we deduced that the cultivated Zanthoxylum species may originate in Zhouqu County, Gansu Province, China. Meanwhile, our research provided a scientific basis for the identification and breeding programs of Chinese Zanthoxylum species.

The species of Oxytropis DC. of section Gloeocephala Bunge (Fabaceae) from Northeast Asia: genetic diversity and relationships based on sequencing of the intergenic spacers of cpDNA and ITS nrDNA

Phylogenetic relationships within Oxytropis DC. sect. Gloeocephala Bunge from Northeast Asia were studied using plastid intergenic spacers (psbA-trnH + trnL-trnF + trnS-trnG) and ITS nrDNA. Populations of O. anadyrensis Vass., O. borealis DC., O. middendorffii Trautv., O. trautvetteri Meinsh., and O. vasskovskyi Jurtz. were monomorphic or characterised by a low level of chloroplast genetic diversity (h varied from 0.143 to 0.692, and π from 0.0001 to 0.0005). Presumably, the low genetic diversity was a result of the severe bottlenecks during Pleistocene glaciation-interglacial cycles. Twenty chlorotypes were identified; species studied had no shared chlorotypes. Chlorotypes of O. anadyrensis, O. borealis, and O. middendorffii formed two lineages each, while the chlorotypes of O. trautvetteri and O. vasskovskyi formed one separate lineage each in the phylogenetic network. There were specific diagnostic markers of cpDNA in each lineage, excluding O. vasskovskyi. The presence of a species-specific diagnostic marker in O. trautvetteri and specific markers in two lineages of O. anadyrensis support circumscribing these taxa as independent species. Regarding ITS nrDNA polymorphism, five ribotypes were detected. The differences revealed in plastid and nuclear genomes of Oxytropis sect. Gloeocephala confirmed that the Asian sector of Megaberingia was the main centre of diversification of arctic legumes.

Genetic diversity of Oxytropis section Xerobia (Fabaceae) in one of the centres of speciation

The genetic diversity and phylogenetic relationships of Oxytropis caespitosa, O. grandiflora, O. eriocarpa, O. mixotriche, O. nitens, O. peschkovae and O. triphylla, section Xerobia subgenus Oxytropis, in one of the main speciation centres of the genus Oxytropis (Baikal Siberia and adjacent territories of Northeastern Mongolia) were studied based on sequence analysis of the psbA-trnH, trnL-trnF and trnS-trnG intergenic spacers of cpDNA, as well as the ITS nrDNA. Most populations are characterized by a high level of chloroplast genetic diversity (h varied from 0.327 to 1.000 and π from 0.0001 to 0.0090) due to the ancient origin for some species and to hybridization and polyploidy for others. 67 haplotypes were identified, of which six were shared. Phylogenetic relationships among species could not be satisfactorily resolved. Only the haplotypes of O. triphylla formed a group with rather high support. Probably, O. caespitosa, O. grandiflora, O. mixotriche and O. nitens constitute a single genetic complex. As regards the ITS nrDNA polymorphism, we detected only two ribotypes (RX1, RX2). Both were found in O. caespitosa, O. eriocarpa, O. mixotriche and O. peschkovae, while RX1 was present in O. nitens and O. triphylla, RX2 in O. grandiflora. The absence of diagnostic species-specific variants for the markers studied, together with the sharing of cpDNA haplotypes and nrDNA ribotypes between species, and the resulting polytomies on the phylogenetic trees, confirm the hypothesis on the hybrid origin of some of them. Obviously, the reproductive barriers within the sect. Xerobia are weak. However, morphological differences between the species of the sect. Xerobia are clearly pronounced, even when they grow in sympatry.