The Complete Chloroplast Genomes of Three Manglietia Species and Phylogenetic Insight into the Genus Manglietia Blume.

Abstract

The genus Manglietia Blume is an important group of Magnoliaceae that has high economic and ornamental value. Owing to the small morphological differences among most Manglietia species and the limited sample sizes in previous molecular-level studies, its infrageneric classification remains unclear, and interspecific relationships for some species are still contentious. Clarifying the phylogenetic relationships within the genus Manglietia is crucial for species classification, genetic diversity assessment, and evolutionary developmental studies. This study sequenced, assembled, and annotated the chloroplast (cp) genomes of Manglietia guangnanica, Manglietia hookeri, and Manglietia longirostrata. The results indicated that these cp genomes are canonical quadripartite structures with total lengths of 160,067 bp, 160,067 bp, and 160,076 bp, respectively. All three cp genomes were annotated with 133 genes, comprising 88 protein-coding genes, 37 tRNAs, and 8 rRNAs. A total of 31, 30, and 30 dispersed repeats and 53, 53, and 56 SSRs were detected, respectively. ENC plot, neutrality plot, and PR2 plot analyses indicated that codon usage bias was influenced primarily by natural selection. Nucleotide diversity analysis revealed 8 highly variable regions in the cp genomes, among which petA-psbJ, rpl32-trnL, and ccsA-ndhD are recommended as candidate molecular markers for Manglietia species. Phylogenetic analysis revealed four highly supported clades: Clade I (18 species), Clade II (M. decidua only), Clade III (9 species), and Clade IV (M. caveana only). Among these clades, Clade IV is a newly discovered monotypic clade in this study, which differs from the results of all previous studies. Further investigations of Clades I and III, which include multiple Manglietia species, revealed that the presence or absence of hairs on Twigs, Stipules, and the abaxial surface of the leaf are important morphological characteristics for distinguishing species between these two clades. Furthermore, the results revealed that M. guangnanica and M. calcarea are two distinct species, and the treatment of M. longirostrata as a variety of M. hookeri was not supported by our study. This study enriches the cp genome data of Manglietia, provides new insights into infrageneric classification, and lays a foundation for further phylogenetic and evolutionary studies of Manglietia.