Advancements in Molecular Marker Development for Medicinal Salvia

Yang Liu^*
*Correspondence: Yang Liu, Department of Medical Sciences, Peking Union Medical College, Beijing, China, Email:

Keywords

Salvia bowleyana • Salvia splendens • Salvia officinalis

Introduction

The Lamiaceae family, which ranks as the sixth-largest among flowering plant families, encompasses a rich diversity of life. Within this family, there are approximately 3,500 species distributed across 220 genera and further classified into 10 subfamilies [1]. The primary distribution of these species spans across Asia, Europe, and Africa. Historically, the Lamiaceae family shares its closest connections with the Verbenaceae and Violinaceae families [2].

In the expansive realm of the Lamiaceae family, China alone hosts more than 800 species and 99 genera, with a remarkable 1,050 Salvia species. Among these, 32 variations and 78 distinct species thrive predominantly in tropical or temperate regions [3]. Taxonomically, the Salvia genus has undergone several evolutionary categorizations. Bentham and Briquet, for instance, divided it into four subgenera and 12 groupings. Furthermore, American scientist Carl Epling dissected the subgenus Calosphace into an astonishing 91 groups, expanding the genus to 102 groups within the following two decades. Geographically, the Salvia genus exhibits variation, with five groups in the European flora, contrasting with four subgenera and eight groups in the flora spanning the USSR, Africa, and Europe. In East Asia, the Chinese Salvia genus was meticulously categorized into five subgenus groups and 18 subbranches by the esteemed botanist, academician Wu Zhengyi.

However, it's worth noting that the Salvia genus is not monophyletic, as evidenced by molecular data from rbcL and trnL-F sequences. This genus shares a sister taxon relationship with other genera such as Rosmarinus, Perovskia, Dorystaechas, Meriandra, and Zhumeria. Moreover, genetic systematics and morphological evidence have led to the formal inclusion of 15 species from the genera Rosmarinus, Perovskia, Spear, Meriandra, and Zhumeria within the broader Salvia genus, revealing ten distinct clades.

The diversity within the Salvia genus is not limited to geography and morphology but extends to genetic makeup. The divergence of Salvia species in Japan, for example, groups 11 species into a single branch based on rbcL, trnL-F, and ITS sequences. Meanwhile, the classification of 38 Salvia species in China using ITS, rbcL, psbA-trnH, and matK sequences challenges the monophyly of the three subgenera previously defined in Chinese plants.

Literature Review

East Asian Salvia, as confirmed by a phylogenetic tree featuring 78 species and 10 variants, forms a monophyletic group, officially designated as Clade IV and is further divided into eight groups. This classification was established through a comprehensive study of ITS, ETS, psbA-trnH, ycf1-rps15, and trnLtrnF sequences.

Beyond phylogeny, the Salvia genus's significance extends to its phytochemical components and their therapeutic properties, assessed through NRI and NTI metrics. Salvia boweyara, for instance, has demonstrated effectiveness in managing hepatic and reproductive issues. Consequently, variations within Salvia species encompass morphological traits, chemical compositions, therapeutic effects, and molecular markers. To elucidate the Salvia genus's position within the Lamiaceae family, a holistic approach to taxonomic research is warranted [4].

Switching gears to plant organelles, the chloroplast stands as the paramount entity in plants. It houses numerous genes critical for photosynthesis, evolutionary processes, and genetic engineering. The chloroplast genome encodes over 120 genes, classified into three categories: those associated with photosynthesis, biosynthesis of fatty acids and amino acids, and transcription and translation. Notably, genes linked to photosystems I (PSA) and II are dispersed within the large-single copy (LSC) and small single copy (SSC) regions, such as PSB, alongside tRNA, ATP enzyme, NADH plastid-masking oxidoreductase, and RNA polymerase genes. Additionally, major subunits of Rubisco, encoded by rbcL, are present. The inverted repeat (IR) region mainly comprises genes for rRNA (RPS), including 16S and 23S genes. Intermediate genes encode 4.5S rRNA, 5S rRNA, 2 tRNA, and several genes with undefined functions.

Chloroplast genomes offer a treasure trove of genes suitable for applications ranging from species identification and phylogenetic analysis to genetic modification and molecular breeding of medicinal plants. These genomes, including psbA-trnH, matK, and rbcL, have been extensively utilized for DNA-based molecular identification, allowing the analysis of polymorphic loci containing multiple genes and gene spacers. While 14 Salvia species within the Lamiaceae family have had their chloroplast genomes documented, the comprehensive exploration of chloroplast genomes presents a foundational resource for investigating structural variations, traits, genetic evolution, and chemistry. In a concerted effort to pinpoint phylogenetic genome regions of divergence and assess the potential of phylogenomics in unraveling the evolutionary and systematic relationships within the Salvia genus of the Lamiaceae family, we have undertaken the pioneering sequencing and analysis of chloroplast genomes for three Salvia species.

Discussion

Distinguishing among the ten Salvia species becomes comprehensible when we delve into the DNA sequences found within the highly variable regions. A comparison of chloroplast genomes in three distinct intergenic spacer (IGS) regions, namely rps16-trnQ-UUG, trnL-UAA-trnF-GAA, and trnM(cau)-atpE, facilitates this differentiation. These Salvia species, namely S. officinalis, S. japonica, S. sclarea, S. meiliensis, S. hispanica, S. tiliifolia, S. yangii, S. splendens, S. nilotica, and S. chanryoenica, can be distinguished based on these genetic markers. Notably, the first IGS region is shared with species belonging to the Zingiber officinale and Coffeae alliance, while the second one is a common occurrence among angiosperms. The third region has evolved over time and has historical ties to both gymnosperms and angiosperms, with some of the oldest mitochondrial DNA (mtDNA) segments, including trnV(uac)- trnM(cau)-atpE-atpB-rbcL, being transferred from chloroplast DNA (cpDNA) to mtDNA. Additionally, to reconstruct the evolutionary relationships within the Eurystachys clade, nuclear ribosomal DNA sequences (nrETS, 5S-NTS) from a diverse pool of 148 accessions were employed. This investigation encompassed genera with well-defined distinctions, such as Prasium and Sideritis [5,6].

Conclusion

Utilizing advanced Illumina sequencing technology, we successfully obtained the complete chloroplast genomes of three distinct Salvia species: S. bowleyana, S. splendens, and S. officinalis. These species exhibit distinctive phenotypic traits, facilitating straightforward differentiation among them. Through phylogenetic analysis, we established that these three species occupy separate branches within a broader grouping comprising 23 Salvia species and the Rosmarinus genus. The examination of seven intergenic spacer (IGS) regions, namely rps16-trnQ-UUG, trnL-UAA-trnF-GAA, trnMCAU- atpE, trnL-UAG-ccsA, ccsA-ndhD, rps15-ycf1, and ndhE-ndhG, revealed significant sequence divergence among these species. Notably, the three Salvia species in focus shared commonalities in two specific IGS regions: trnG-GCC-trnM-CAU and ycf3-trnS-GGA. The remarkable diversity observed in these sequence divergences suggests their potential utility as valuable DNA markers for future identification and phytotaxonomy of the Salvia genus. Collectively, the information acquired through this study promises to advance our understanding of Salvia taxonomy, ecology, phylogenetic evolution, and conservation efforts within the Chinese context.

Acknowledgement

None.

Conflict of Interest

None.

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