Abstract
Beech trees of the genus Fagus (Fagaceae) are monoecious and distributed in the Northern Hemisphere. They represent an important component of mixed broad-leaved evergreen–deciduous forests and are an economically important source of timber. Despite their ecological and economical importance, however, little is known regarding the overall plastome evolution among Fagus species in East Asia. In particular, the taxonomic position and status of F. multinervis, a beech species endemic to Ulleung Island of Korea, remains unclear even today. Therefore, in this study, we characterized four newly completed plastomes of East Asian Fagus species (one accession each of F. crenata and F. multinervis and two accessions of F. japonica). Moreover, we performed phylogenomic analyses comparing these four plastomes with F. sylvatica (European beech) plastome. The four plastomes were highly conserved, and their size ranged from 158,163 to 158,348 base pair (bp). The overall GC content was 37.1%, and the sequence similarity ranged from 99.8% to 99.99%. Codon usage patterns were similar among species, and 7 of 77 common protein-coding genes were under positive selection. Furthermore, we identified five highly variable hotspot regions of the Fagus plastomes (ccsA/ndhD, ndhD/psaC, ndhF/rpl32, trnS-GCU/trnG-UCC, and ycf1). Phylogenetic analysis revealed the monophyly of Fagus as well as early divergence of the subgenus Fagus and monophyletic Engleriana. Finally, phylogenetic results supported the taxonomic distinction of F. multinervis from its close relatives F. engleriana and F. japonica. However, the sister species and geographic origin of F. multinervis on Ulleung Island could not be determined.
Highlights
Introduction(Fagaceae), commonly distributed in the Northern Hemisphere, is an ecologically and economically important tree lineage of broad-leaved deciduous-evergreen forests of North America and East Asia as well as the most abundant broad-leaved tree genus in Europe and West Asia [1,2,3,4]
Genus Fagus L. (Fagaceae), commonly distributed in the Northern Hemisphere, is an ecologically and economically important tree lineage of broad-leaved deciduous-evergreen forests of North America and East Asia as well as the most abundant broad-leaved tree genus in Europe and West Asia [1,2,3,4].With the center of diversity in East Asia, Fagus comprises 10 monoecious broad-leaved deciduous tree species within two subgenera, namely Engleriana and Fagus [1,5].While subgenus Engleriana is restricted to East Asia (China, Korea, and Japan), Fagus is distributed almost throughout the Northern Hemisphere
Engleriana are endemic to Japan, while F. engleriana Seemen is distributed in China; the taxonomic entity of F. okamotoi is uncertain in Japan and it is not currently recognized as a distinct species
Summary
(Fagaceae), commonly distributed in the Northern Hemisphere, is an ecologically and economically important tree lineage of broad-leaved deciduous-evergreen forests of North America and East Asia as well as the most abundant broad-leaved tree genus in Europe and West Asia [1,2,3,4]. While subgenus Engleriana is restricted to East Asia (China, Korea, and Japan), Fagus is distributed almost throughout the Northern Hemisphere. Engleriana are endemic to Japan, while F. engleriana Seemen is distributed in China; the taxonomic entity of F. okamotoi is uncertain in Japan and it is not currently recognized as a distinct species. Of the seven species of subgenus Fagus, F. sylvatica L. is widely distributed in Europe and southwestern. Some species are geographically restricted to specific regions, such as F. crenata Blume to Japan, F. longipetiolata Seemen and F. lucida Rehder and Wilson to China, and F. chienii Cheng to western China. F. okamotoi has been recorded from few localities in Japan, while F. chienii is recorded from a single locality in western
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