Exploring the Complete Chloroplast Genomes of Key Lamiaceae Species Uncovers the Secrets of Evolutionary Dynamics and Phylogenetic Relationships

Abstract

Chloroplast genome analysis provides crucial insights into plant evolution, classification, and conservation strategies. This study aimed to conduct a comprehensive comparative analysis of chloroplast genome architecture, gene content, and evolutionary relationships among five species of Lamiaceae (Lavandula angustifolia, Mentha x piperita, Ocimum x africanum, Salvia japonica, and Thymus serpyllum). Complete chloroplast genome sequences were retrieved from the NCBI database and analyzed using a systematic bioinformatics pipeline. Genome annotation was performed using Geneious Prime software, while repetitive sequence analysis was conducted using Tandem Repeats Finder. Phylogenetic relationships were reconstructed using MEGA software, implementing both the DualBrothers model and Neighbor-Joining method. The analyzed genomes exhibited the characteristic quadripartite structure, with sizes ranging from 152,048 to 153,995 base pairs and GC content between 37.8 and 38.0%. Each genome contained 131-134 genes, including 50 protein-coding sequences, 8 rRNA genes, and 37 tRNA genes. Comparative analysis revealed region-specific GC content variations, with IR regions showing the highest (43.0-43.4%), followed by LSC (35.9-36.2%) and SSC regions (31.6-32.1%). Codon usage analysis demonstrated a significant bias toward T/C-ending codons, particularly TTT, AAA, and AAT, correlating with the high AT content. Notable variations were observed at the LSC/IR/SSC junction regions, attributed to IR expansion and contraction. Molecular clock analyses indicated consistent evolutionary rates across the studied species. These findings provide valuable insights into the molecular evolution of Lamiaceae chloroplast genomes and establish a foundation for future research in plant molecular biology, systematic studies, and conservation efforts.