Background: Styrax, a vital raw material for shipbuilding, construction, perfumes, and drugs, represents the largest and most diverse genus in the Styracaceae. However, there is a relative scarcity of research on Styrax, particularly in evolution and genetics. Therefore, this study conducted comparative and evolutionary analyses of the chloroplast genomes of five rare Styrax species (S. argentifolius, S. buchananii, S. chrysocarpus, S. finlaysonianus, and S. rhytidocarpus). Results: The results indicated that, despite high levels of conservation in chloroplast genome structure among these species, specific mutation hotspot regions exist, particularly involving the expansion and contraction of the IR region. Additionally, evidence of positive selection was detected in eight genes (atpB, ccsA, ndhD, petA, rbcL, rpoC1, ycf1, and ycf2), which may be associated with adaptive evolution in response to environmental changes. Phylogenetic analysis revealed conflicts between trees constructed based on coding sequences and complete chloroplast genomes for several species, which were similar to previous phylogenetic studies. Conclusion: This study underscores the importance of increasing sample sizes to enhance the accuracy of phylogenetic analyses and provides a new perspective on understanding the adaptive evolution of Styrax species. These findings are not only important for the conservation and sustainable use of Styrax, but also provide valuable insights for research in plant evolution and ecology within the genus.

Styrax japonicus is a medicinal and ornamental shrub belonging to the Styracaceae family. To explore the diversity and characteristics of the chloroplast genome of S. japonicus, we conducted sequencing and comparison of the chloroplast genomes of four naturally distributed S. japonicus. The results demonstrated that the four chloroplast genomes (157,914–157,962 bp) exhibited a typical quadripartite structure consisting of a large single copy (LSC) region, a small single copy (SSC) region, and a pair of reverse repeats (IRa and IRb), and the structure was highly conserved. DNA polymorphism analysis revealed that three coding genes (infA, psbK, and rpl33) and five intergene regions (petA-psbJ, trnC-petN, trnD-trnY, trnE-trnT, and trnY-trnE) were identified as mutation hotspots. These genetic fragments have the potential to be utilized as DNA barcodes for future identification purposes. When comparing the boundary genes, a small contraction was observed in the IR region of four S. japonicus. Selection pressure analysis indicated positive selection for ycf1 and ndhD. These findings collectively suggest the adaptive evolution of S. japonicus. The phylogenetic structure revealed conflicting relationships among several S. japonicus, indicating divergent evolutionary paths within this species. Our study concludes by uncovering the genetic traits of the chloroplast genome in the differentiation of S. japonicus variety, offering fresh perspectives on the evolutionary lineage of this species.

Ehretia dicksonii_Hance 1862 is a deciduous botany of Ehretiaceae. In this work, the complete chloroplast (cp) genome sequence of E. dicksonii was probed by next generation sequencing in an effort to provide genomic resources useful for promoting its conservation. The complete cp genome of E. dicksonii is 156,623 bp in length, including a large single-copy (LSC) region of 86,853 bp, and a small single-copy (SSC) region of 18,150 bp. It contains 133 genes, including 37 tRNA genes, 8 rRNA genes, and 88 protein-coding genes. The overall GC content of E. dicksonii chloroplast genome is 37.85%. The phylogenetic analysis suggests that E. dicksonii is in the clade of Ehretiaceae other than Boraginaceae. Also, E. dicksonii has a close relationship with Ehretia acuminata_Brown 1810 in Ehretiaceae.

Thunbergia erecta (Benth.) T. Anders. is an upright shrub species of Acanthaceae with great ecological and economical values. In this paper, we explored the complete chloroplast genome sequence of T. erecta using next generation sequencing to provide genomic resources that could help to promote its conservation. The genome of T. erecta is 152,202 bp in length, containing a large single-copy region of 84,232 bp, and a small single-copy region of 17,656 bp. It encodes a total of 131 genes, including 8 rRNA genes, 37 tRNA genes, 84 protein-coding genes and 2 pseudo genes. The GC content of T. erecta genome is 38.47%. The phylogenetic analysis suggests that it was closely related to Avicennia marina in Acanthaceae. In addition, we found that T. erecta appeared late clade in the whole family while outgroups plants appeared even later. T. erecta is morphologically similar to other plants in Acanthaceae, but is genetically closed to the outgroup species.

Melliodendron xylocarpum is a member of the Styracaceae family, which is well-known for its remarkable ornamental and medicinal properties. In this research, we conducted comparative analysis of the chloroplast genomes from four samples of M. xylocarpum, representing Melliodendron. The results demonstrated that the chloroplast genome of four M. xylocarpum samples ranging from 157,103 bp to 158,357 bp exhibited a typical quadripartite structure, including one large single-copy (LSC) region (90,131 bp to 90,342 bp), one small single-copy (SSC) region (18,467 bp to 18,785 bp), and two inverted repeat regions (IRs) (24,115 bp to 24,261 bp). Different levels of expansion and contraction were observed in the IR region of four M. xylocarpum samples. Besides, accD and ycf1 have been identified under positive selection, potentially linked to the adaptive response of Melliodendron to various environmental changes. Conflicting phylogenetic relationships were identified among various genera within the Styracaceae family in the phylogenetic tree constructed using CDS sequences and complete chloroplast genomes. Furthermore, the significance of a large sample size was also highlighted in this study for enhancing the accuracy of findings from phylogenetic analyses. The findings of this research will provide significant insights for future investigations into the evolutionary trends and conservation of the Melliodendron species.

"Yan Zi: A New Styrax japonicas Cultivar" published on Dec 2024 by American Society for Horticultural Science.