Comparative genomics and phylogenetic analysis of three Malvaceae species on the basis of chloroplast genomes
The Malvaceae family shows rich species diversity and has substantial economic and medicinal value. However, the frequent interspecific hybridization among members of this family has resulted in confused phylogenetic relationships among the groups, limiting the usefulness of traditional classification methods. This study aimed to investigate the phylogenetic relationships among selected taxa of Malvaceae by evaluating 23 chloroplast (CP) genomes, including three newly assembled CP genomes. Among these three genomes, the CP genome of Hibiscus schizopetalus L. was reported for the first time, while the CP genomes of Alcea rosea L. and Hibiscus grewiifolius L., which have been deposited in NCBI, were re-analyzed here alongside newly generated data for comparative purposes. In addition, 20 downloaded CP genomes encompassing 13 genera were analyzed using SNPs in whole CP genomes data. The results showed that the genomes ranged from 160,403 to 161,978 base pairs in length and consisted of small single copies (SSCs) and large single copies (LSCs) separated by two inverted repeat sequences (IRs), forming a typical quadripartite circular structure. The entire genome sequence showed relative conservation across species in terms of structure, GC content, codon usage, and gene composition. The mutation sites were mainly located in the LSC and SSC regions, and the variability in the non-coding regions was higher than that in the coding regions. The nucleotide polymorphism (Pi) analysis identified the non-coding regions such as ndhF-rpl32 and psbZ-trnG as high variable hotspots. A maximum likelihood phylogenetic tree was constructed based on SNPs in whole CP genomes data. The phylogenetic analysis divided these 23 species into five highly supported clades. It also revealed a close sister-group relationship between Abelmoschus and Hibiscus species, suggesting that Hibiscus may have a separate lineage from okra species. In conclusion, the increasing availability of CP genome resources will enhance our understanding of the classification and evolutionary patterns of the Malvaceae family. The development of molecular markers will provide important molecular evidence for precise identification and classification revision of plants in this family.