Torreya Arn., an important genus of Taxaceae, has six species occurring in North America and eastern Asia. Species in Torreya are economic cultivation in South China for a long time, especially in Zhejiang province. Most of Torreya species are in endangered due to the forest destruction and overdevelopment. Despite both morphological and molecular evidence supporting monophyletic of Torreya, the phylogenetic relationships among species remains controversial. 

The discontinuous flora between East Asia and Norther America has drawn much attention to biologists and ecologists. Gymnosperms may provide a better resolution for exploring the geographical association between East Asian and North American flora due to their early origination. Based on the investigation of Torreya resources, the research group led by Prof. WANG Hengchang from Wuhan Botanical Garden carried out a comprehensive sampling and conducted a phylogenomic and biogeographic study of Torreya using plastomes. 

Whole plastomes have become easily accessible with the explosive development of next-generation sequencing technologies. They can provide abundant informative sites for phylogenetic analyses in resolving difficult relationships at broad taxonomic levels. Moreover, comparative genomic studies on the basis of plastomes have provided insights into the molecular evolutionary patterns associated with structure variations in genomes.  

All sequenced Torreya plastomes share the same complement of 82 protein-coding genes, four ribosomal RNA genes, and 31 transfer RNA genes. Different from the typical quadripartite structure shared by most angiosperm plastomes, the plastomes of Torreya are characterized with the loss of an inverted repeat (IR). Phylogenomic analysis provides well-supported resolution and robust supports of relationships within Torreya.  

The biogeographic study reveals that the dispersals across Bering Land Bridge at the Late Miocene and subsequent vicariances in the Quaternary may shape the current distributions of Torreya.  

Based on the obust phylogenetic topology and reliable calibration point, we preliminarily resolved the evolutionary history of the importance gymnosperm genus Torreya. The study highlights the efficiency of whole plastome sequences for phylogenetic analysis. This study not only has great academic significance, but also provides a theoretical basis for the identification and conservation of economic plant resources. 

This work was supported by the National Natural Science Foundation of China, the Programme Foundation for the Backbone of Scientific Research by Wuhan Botanical Garden and National Key R&D Program of China Foundation. Relevant research results have been published in Journal of Systematics and Evolution entitled “Plastome phylogenomic analysis of Torreya (Taxaceae)”. 

Ancestral reconstruction of Torreya by RASP. A, China; B, Japan; C, western North America; D, eastern North America. (Image by ZHANG Xu)