Phylogenomics, plastome structure and species identification in Mahonia (Berberidaceae)

Chloroplast genome evolution of Berberis (Berberidaceae): Implications for phylogeny and metabarcoding

Berberidis Radix (Sankezhen), a typical multi-origin Chinese medicinal material, originates from the dried roots of plants of the Berberis genus and is used to treat various ailments. These species have similar morphologies, potentially leading to misidentifications that can impact medicine efficacy. Therefore, developing suitable molecular markers to identify medicinal species is imperative. Furthermore, discrepancies exist in the taxonomy of the Berberis genus. In the present study, we de novo assembled the chloroplast genomes of six Berberis species (Berberis woomungensis C. Y. Wu, Berberis pruinosa Franch., Berberis thunbergii DC., Berberis chinensis Poir., Berberis wilsoniae Hemsl., and Berberis sp.) that commonly constitute Berberidis Radix and compared them with previously reported genomes. Our comparative analysis revealed similarities in genome structure, relative synonymous codon usage, amino acid frequency, repeats, and substitutions. Higher synonymous substitutions, indicative of predominant purifying selection on protein-coding genes, were observed compared to non-synonymous substitutions. However, positive selection was identified in six genes across 29 Berberis species-accD, matK, ndhD, rbcL, ycf1, and ycf2-highlighting their potential roles in adaptive responses to specific environmental conditions within the genus. Inverted repeats expansion and contraction affected the rate of mutations and were associated with the phylogenetic classification of Berberis. Our phylogenetic analysis supported the division of the Berberis complex into four genera, which corroborates previous studies involving extensive sampling. We identified the ndhD-ccsA region as the most polymorphic region and applied this region to Chinese patent medicines containing Berberidis Radix through metabarcoding. The metabarcoding analysis confirmed that five Berberis species commonly constitute Berberidis Radix in Chinese patent medicines. In conclusion, this study provides insight into the molecular evolution of the chloroplast genome and the phylogeny of the Berberis genus. In addition, metabarcoding provides insight into the species composition of Berberidis Radix in Chinese patent medicines.

Population structure and diversification of Gymnospermium kiangnanense, a plant species with extremely small populations endemic to eastern China

Background

Gymnospermium kiangnanense is the only species distributed in the subtropical region within the spring ephemeral genus Gymnospermium. Extensive human exploitation and habitat destruction have resulted in a rapid shrink of G. kiangnanense populations. This study utilizes microsatellite markers to analyze the genetic diversity and structure and to deduce historical population events of extant populations of G. kiangnanense.

Methods

A total of 143 individuals from eight extant populations of G. kiangnanense, including two populations from Anhui Province and six populations from Zhejiang Province, were analyzed with using 21 pairs of microsatellite markers. Genetic diversity indices were calculated using Cervus, GENEPOP, GenALEX. Population structure was assessed using genetic distance (UPGMA), principal coordinate analysis (PCoA), Bayesian clustering method (STRUCTURE), and molecular variation analysis of variance (AMOVA). Population history events were inferred using DIYABC.

Results

The studied populations of G. kiangnanense exhibited a low level of genetic diversity (He = 0.179, I = 0.286), but a high degree of genetic differentiation (FST = 0.521). The mean value of gene flow (Nm ) among populations was 1.082, indicating prevalent gene exchange via pollen dispersal. Phylogeographic analyses suggested that the populations of G. kiangnanense were divided into two lineages, Zhejiang (ZJ) and Anhui (AH). These two lineages were separated by the Huangshan-Tianmu Mountain Range. AMOVA analysis revealed that 36.59% of total genetic variation occurred between the two groups. The ZJ lineage was further divided into the Hangzhou (ZJH) and Zhuji (ZJZ) lineages, separated by the Longmen Mountain and Fuchun River. DIYABC analyses suggested that the ZJ and AH lineages were separated at 5.592 ka, likely due to the impact of Holocene climate change and human activities. Subsequently, the ZJZ lineage diverged from the ZJH lineage around 2.112 ka. Given the limited distribution of G. kiangnanense and the significant genetic differentiation among its lineages, both in-situ and ex-situ conservation strategies should be implemented to protect the germplasm resources of G. kiangnanense.

Comparative plastome analysis of the sister genera Ceratocephala and Myosurus (Ranunculaceae) reveals signals of adaptive evolution to arid and aquatic environments

BACKGROUND

Expansion and contraction of inverted repeats can cause considerable variation of plastid genomes (plastomes) in angiosperms. However, little is known about whether structural variations of plastomes are associated with adaptation to or occupancy of new environments. Moreover, adaptive evolution of angiosperm plastid genes remains poorly understood. Here, we sequenced the complete plastomes for four species of xerophytic Ceratocephala and hydrophytic Myosurus, as well as Ficaria verna. By an integration of phylogenomic, comparative genomic, and selection pressure analyses, we investigated evolutionary patterns of plastomes in Ranunculeae and their relationships with adaptation to dry and aquatic habitats.

RESULTS

Owing to the significant contraction of the boundary of IRA/LSC towards the IRA, plastome sizes and IR lengths of Myosurus and Ceratocephala are smaller within Ranunculeae. Compared to other Ranunculeae, the Myosurus plastome lost clpP and rps16, one copy of rpl2 and rpl23, and one intron of rpoC1 and rpl16, and the Ceratocephala plastome added an infA gene and lost one copy of rpl2 and two introns of clpP. A total of 11 plastid genes (14%) showed positive selection, two genes common to Myosurus and Ceratocephala, seven in Ceratocephala only, and two in Myosurus only. Four genes showed strong signals of episodic positive selection. The rps7 gene of Ceratocephala and the rpl32 and ycf4 genes of Myosurus showed an increase in the rate of variation close to 3.3 Ma.

CONCLUSIONS

The plastomic structure variations as well as the positive selection of two plastid genes might be related to the colonization of new environments by the common ancestor of Ceratocephala and Myosurus. The seven and two genes under positive selection might be related to the adaptation to dry and aquatic habitats in Ceratocephala and Myosurus, respectively. Moreover, intensified aridity and frequent sea-level fluctuations, as well as global cooling, might have favored an increased rate of change in some genes at about 3.3 Ma, associated with adaptation to dry and aquatic environments, respectively. These findings suggest that changing environments might have influenced structural variations of plastomes and fixed new mutations arising on some plastid genes owing to adaptation to specific habitats.

Extreme Reconfiguration of Plastid Genomes in Papaveraceae: Rearrangements, Gene Loss, Pseudogenization, IR Expansion, and Repeats

The plastid genomes (plastomes) of angiosperms are typically highly conserved, with extreme reconfiguration being uncommon, although reports of such events have emerged in some lineages. In this study, we conducted a comprehensive comparison of the complete plastomes from twenty-two species, covering seventeen genera from three subfamilies (Fumarioideae, Hypecooideae, and Papaveroideae) of Papaveraceae. Our results revealed a high level of variability in the plastid genome size of Papaveraceae, ranging from 151,864 bp to 219,144 bp in length, which might be triggered by the expansion of the IR region and a large number of repeat sequences. Moreover, we detected numerous large-scale rearrangements, primarily occurring in the plastomes of Fumarioideae and Hypecooideae. Frequent gene loss or pseudogenization were also observed for ndhs, accD, clpP, infA, rpl2, rpl20, rpl32, rps16, and several tRNA genes, particularly in Fumarioideae and Hypecooideae, which might be associated with the structural variation in their plastomes. Furthermore, we found that the plastomes of Fumarioideae exhibited a higher GC content and more repeat sequences than those of Papaveroideae. Our results showed that Papaveroideae generally displayed a relatively conserved plastome, with the exception of Eomecon chionantha, while Fumarioideae and Hypecooideae typically harbored highly reconfigurable plastomes, showing high variability in the genome size, gene content, and gene order. This study provides insights into the plastome evolution of Papaveraceae and may contribute to the development of effective molecular markers.

Phylogenomics and plastome evolution of Indigofera (Fabaceae)

Introduction

Indigofera L. is the third largest genus in Fabaceae and includes economically important species that are used for indigo dye-producing, medicinal, ornamental, and soil and water conservation. The genus is taxonomically difficult due to the high level of overlap in morphological characters of interspecies, fewer reliability states for classification, and extensive adaptive evolution. Previous characteristic-based taxonomy and nuclear ITS-based phylogenies have contributed to our understanding of Indigofera taxonomy and evolution. However, the lack of chloroplast genomic resources limits our comprehensive understanding of the phylogenetic relationships and evolutionary processes of Indigofera.

Methods

Here, we newly assembled 18 chloroplast genomes of Indigofera. We performed a series of analyses of genome structure, nucleotide diversity, phylogenetic analysis, species pairwise Ka/Ks ratios, and positive selection analysis by combining with allied species in Papilionoideae.

Results and discussion

The chloroplast genomes of Indigofera exhibited highly conserved structures and ranged in size from 157,918 to 160,040 bp, containing 83 protein-coding genes, 37 tRNA genes, and eight rRNA genes. Thirteen highly variable regions were identified, of which trnK-rbcL, ndhF-trnL, and ycf1 were considered as candidate DNA barcodes for species identification of Indigofera. Phylogenetic analysis using maximum likelihood (ML) and Bayesian inference (BI) methods based on complete chloroplast genome and protein-coding genes (PCGs) generated a well-resolved phylogeny of Indigofera and allied species. Indigofera monophyly was strongly supported, and four monophyletic lineages (i.e., the Pantropical, East Asian, Tethyan, and Palaeotropical clades) were resolved within the genus. The species pairwise Ka/Ks ratios showed values lower than 1, and 13 genes with significant posterior probabilities for codon sites were identified in the positive selection analysis using the branch-site model, eight of which were associated with photosynthesis. Positive selection of accD suggested that Indigofera species have experienced adaptive evolution to selection pressures imposed by their herbivores and pathogens. Our study provided insight into the structural variation of chloroplast genomes, phylogenetic relationships, and adaptive evolution in Indigofera. These results will facilitate future studies on species identification, interspecific and intraspecific delimitation, adaptive evolution, and the phylogenetic relationships of the genus Indigofera.