Study of the genus Torreya (Taxaceae) based on chloroplast genomes

Background: Species of the genus Torreya are similar in morphology, and their morphological taxonomic characteristics are not stable because of environmentally induced changes. Therefore, morphology is insufficient for understanding their relationships. Chloroplast genome sequencing technology provides a powerful tool for molecular analysis to get more infomation for classification and identification of Torreya genus. Methods: A total of 4 chloroplast genome of Torreya, including T. Parvifolia, T. nucifera, T. fargesii var. Yunnanensis and T. grandis var. jiulongshanensis, were sequenced and annotated. Campartive genome and phylogenetic tree were provided for variation analysis. Results: The chloroplast genome size of the four samples is about 137 kb, the inverted repeat (IR) regions are identified in the genus Torreya. Genome comparison using mVISTA showed high sequence similarity among different species. Regions with divergence in exon regions include accD, ndhB, ndhF, psbA, psbJ, rpl2, rps3, rps16, rps18, ycf1, and ycf2. The phylogenetic tree based on 73 single-copy genes showed a clearer relationships among different species of Torreya. Conclusions: All genomes of the four Torreya species consist of two short IR regions, and results of the phylogenetic analysis concluded that T. parvifolia should be considered as T. fargesii var. yunnanensis or treated as a sister species. T. grandis var. jiulongshanensis should be treated as a variety of T. grandis according to molecular evidence, supporting the originally published proposal.