Complete plastomes of six species of Wikstroemia (Thymelaeaceae) reveal paraphyly with the monotypic genus Stellera

Abstract

Wikstroemia (Thymelaeaceae) is a diverse genus that extends from Asia to Australia and has been recorded on the Hawaiian Islands. Despite its medicinal properties and resource utilization in pulp production, genetic studies of the species in this important genus have been neglected. In this study, the plastome sequences of six species of Wikstroemia were sequenced and analysed. The plastomes ranged in size between 172,610 bp (W. micrantha) and 173,697 bp (W. alternifolia) and exhibited a typical genome structure consisting of a pair of inverted repeat (IR) regions separated by a large single-copy (LSC) region and a small single-copy (SSC) region. The six plastomes were similar in the 138 or 139 genes predicted, which consisted of 92 or 93 protein-coding genes, 38 tRNA genes, and 8 rRNA genes. The overall GC contents were identical (36.7%). Comparative genomic analyses were conducted with the inclusion of two additional published species of Wikstroemia in which the sequence divergence and expansion of IRs in the plastomes were determined. When compared to the coding sequences (CDSs) of Aquilaria sinensis, five genes, namely, rpl2, rps7, rps18, ycf1 and ycf2, indicated positive selection in W. capitata. The plastome-based phylogenetic analysis inferred that Wikstroemia in its current state is paraphyletic to Stellera chamaejasme, while the ITS-based tree analyses could not properly resolve the phylogenetic relationship between Stellera and Wikstroemia. This finding rekindled interest in the proposal to synonymize Stellera with Wikstroemia, which was previously proposed but rejected due to taxonomic conflicts. Nevertheless, this study provides valuable genomic information to aid in the taxonomic implications and phylogenomic reconstruction of Thymelaeaceae.

Complete chloroplast genome of Daphne pseudomezereum var. koreana (Thymelaeaceae)

“… 2021 ), NC_057149 (unpublished), NC_057996 (He et al. 2021 ), NC_057997 (He et al. 2021 ), NC_057998 (He et al.…”

Extremely high diversity and endemism of chlorotypes in Wikstroemia monnula Hance (Thymelaeaceae) shed light on the effects of habitat heterogeneity on intraspecific differentiation in southeast China

“…PERMUT (Pons & Petit, 1996) was used to calculate and compare the population differentiation indices G ST and N ST . Genealogical relationships of cpDNA haplotypes were estimated parsimoniously using Network4.6.1.1 (Bandelt et al, 1999) using Wikstroemia indica as outgroup based on the phylogeny of Wikstroemia (Zhang et al, 2010; He et al, 2021; Qian et al, 2021; Fig. ).…”

Wikstroemia fragrans (Thymelaeaceae, Daphneae), a new species from Mount Danxia, China based on morphological and molecular evidence

“…The ITS region was used for phylogenetic reconstruction of Wikstroemia. Despite insufficiency in delimiting plants at the species level, the ITS regions of most Wikstroemia species are publicly available and partly provide an insight into phylogenetic relationships between closely related species (He et al 2021;Lee et al 2022). We downloaded all species of Daphneae (Thymelaeaceae) with ITS gene sequences available in NCBI GenBank for analysis.…”