Abstract
Chinese sweetgum (Liquidambar formosana) is a relatively fast-growing ecological pioneer species. It is widely used for multiple purposes. To assess the genetic diversity and genetic differentiation of the species, genic SSR markers were mined from transcriptome data for subsequent analysis of the genetic diversity and population structure of natural populations. A total of 10645 potential genic SSR loci were identified in 80482 unigenes. The average frequency was one SSR per 5.12 kb, and the dinucleotide unit was the most abundant motif. A total of 67 alleles were found, with a mean of 6.091 alleles per locus and a mean polymorphism information content of 0.390. Moreover, the species exhibited a relatively moderate level of genetic diversity (He = 0.399), with the highest was found in population XY (He = 0.469). At the regional level, the southwestern region displayed the highest genetic diversity (He = 0.435) and the largest number of private alleles (n = 5), which indicated that the Southwestern region may be the diversity hot spot of L. formosana. The AMOVA results showed that variation within populations (94.02%) was significantly higher than among populations (5.98%), which was in agreement with the coefficient of genetic differentiation (Fst = 0.076). According to the UPGMA analysis and principal coordinate analysis and confirmed by the assignment test, 25 populations could be divided into three groups, and there were different degrees of introgression among populations. No correlation was found between genetic distance and geographic distance (P > 0.05). These results provided further evidence that geographic isolation was not the primary factor leading to the moderate genetic differentiation of L. formosana. As most of the genetic diversity of L. formosana exists among individuals within a population, individual plant selection would be an effective way to use natural variation in genetic improvement programs. This would be helpful to not only protect the genetic resources but also attain effective management and exploit genetic resources.
Highlights
Chinese sweetgum (Liquidambar formosana Hance) belongs to the genus Liquidambar of family Altingiaceae (Santamour, 1972; Bremer et al, 2009)
These results showed that 4 loci were located in the coding sequence (CDS) regions, 4 loci were located in the 5′ untranslated regions (5′UTR), and the others were located in 3′ untranslated regions (3′-UTR)
The mean frequency of simple sequence repeats (SSR) loci detected in L. formosana was one SSR locus per 5.28 kb, which is lower than that of Larix gmelinii (Zhang et al, 2015), but higher than that of Pinus dabeshanensis (Xiang et al, 2015)
Summary
Chinese sweetgum (Liquidambar formosana Hance) belongs to the genus Liquidambar of family Altingiaceae (Santamour, 1972; Bremer et al, 2009). These disjunctive distributions are remnants of their wide distribution during the Tertiary period This genus had flourished well in a wide area covering East Asia, Central Asia, Asia Minor, America and Central Europe during the Miocene, and disappeared in Europe and Northwest America in the Pleistocene as a result of extensive glaciations (Öztürk et al, 2008). After these glaciations, the natural distributions of Liquidambar species were forced into refugia in East Asia, Turkey and North America (Ozdilek et al, 2012). L. formosana and L. acalycina comprised a special clade in the phylogeny of the genus Liquidambar; the other clade consisted of L. orientalis and L. styraciflua (Li et al, 1997)
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