Abstract
Tribe Forsythieae (Oleaceae), containing two genera (Abeliophyllum and Forsythia) and 13 species, is economically important plants used as ornamentals and in traditional medicine. This tribe species occur primarily in mountainous regions of Eurasia with the highest species diversity in East Asia. Here, we examine 11 complete chloroplast genome and nuclear cycloidea2 (cyc2) DNA sequences of 10 Forsythia species and Abeliophyllum distichum using Illumina platform to provide the phylogeny and biogeographic history of the tribe. The chloroplast genomes of the 11 Forsythieae species are highly conserved, except for a deletion of about 400 bp in the accD–psaI region detected only in Abeliophyllum. Within Forsythieae species, analysis of repetitive sequences revealed a total of 51 repeats comprising 26 forward repeats, 22 palindromic repeats, and 3 reverse repeats. Of those, 19 repeats were common and 32 were unique to one or more Forsythieae species. Our phylogenetic analyses supported the monophyly of Forsythia and its sister group is Abeliophyllum using the concatenated dataset of 78 chloroplast genes. Within Forsythia, Forsythia likiangensis and F. giraldiana were basal lineages followed by F. europaea; the three species are characterized by minutely serrate or entire leaf margins. The remaining species, which are distributed in East Asia, formed two major clades. One clade included F. ovata, F. velutina, and F. japonica; they are morphologically supported by broadly ovate leaves. Another clade of F. suspensa, F. saxatilis, F. viridissima, and F. koreana characterized by lanceolate leaves (except F. suspensa which have broad ovate leaves). Although cyc2 phylogeny is largely congruent to chloroplast genome phylogeny, we find the discordance between two phylogenies in the position of F. ovata suggesting that introgression of the chloroplast genome from one species into the nuclear background of another by interspecific hybridization in East Asian Forsythia species. Molecular dating and biogeographic reconstructions suggest an origin of the Forsythieae species in East China in the Miocene. Distribution patterns in Forsythia indicated that the species were radially differentiated from East China, and the speciation of the European F. europaea was the result of both vicariance and dispersal in the late Miocene to Pliocene.
Highlights
IntroductionAbeliophyllum is a monotypic and endemic genus in Korea characterized by samara-type fruits and white flowers (Kim, 2007)
A deletion of 416 bp in accD–psaI intergenic sequence (IGS) region was identified only in A. distichum, five indels were shared between F. giraldiana and F. likiangensis, and a deletion of 28 bp in ndhF–rpl32 IGS region was observed in three species, F. ovata, F. velutina, and F. japonica
We report the first complete cp genome sequences of 11 species from Abeliophyllum and Forsythia (Forsythieae) (Figure 1 and Table 1)
Summary
Abeliophyllum is a monotypic and endemic genus in Korea characterized by samara-type fruits and white flowers (Kim, 2007). Forsythia consists of 13 locally derived endemic species restricted to certain geographical regions. They are deciduous shrubs characterized by opposite simple or rarely 3-parted to 3-foliolate petiolate leaves, and yellow flowers blooming in the early spring before leaves (Chang et al, 1996; Wu et al, 2010). The fruits of Forsythia suspensa Vahl and F. viridissima Lindl. In light of the need to preserve native species and utilize their genetic information in various phylogenetic and conservational studies, we determined the chloroplast (cp) genome sequences of Forsythieae species
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