Hamamelidaceae, a family of woody plants ranging from tall trees to small shrubs, is an ancient family of approximately 26 genera and 100 species (Endress, 1993). The genera in this family are small: 14 are monotypic, six contain only two to three species, and others are composed of five to 14 species. Furthermore, most species in this family are narrow endemics or are very restricted in their distribution mostly due to past climatic changes (Endress, 1993). Fourteen species of Hamamelidaceae are currently listed as threatened in the IUCN Red List of Threatened Species (IUCN, 2015). To date, only sporadic studies have emphasized the genetic study and conservation of these species (Yu et al., 2014; Hatmaker et al., 2015).

Chunia bucklandioides H. T. Chang (Hamamelidaceae), the only species in Chunia H. T. Chang, was listed as threatened in the IUCN Red List in 1997. It is a tall tree endemic to Hainan, China, and the wood can be applied in agricultural implements, furniture, and construction. However, it is now found only on Mt. Diaoluo and Mt. Jianfeng (IUCN, 2015). Here, we developed and characterized 11 polymorphic expressed sequence tag–simple sequence repeat (EST-SSR) markers and tested their cross-transferability in three related species—Mytilaria laosensis Lecomte, Exbucklandia tonkinensis (Lecomte) H. T. Chang, and E. populnea (R. Br. ex Griff.) R. W. Brown—on the basis of the phylogenetic tree of Hamamelidaceae (Shi et al., 1999). We expect that these markers will be useful for future conservation genetic studies of the species.

METHODS AND RESULTS

The total RNAs were extracted from the fresh leaves of one individual of C. bucklandioides (Mt. Diaoluo; Appendix 1) using the optimized cetyltrimethylammonium bromide (CTAB) method (Gambino et al., 2008). A normalized cDNA library was constructed and sequenced using the HiSeq 2000 system (Illumina, San Diego, California, USA). A total of 55.34 million 100-bp paired-end reads were produced and de novo assembled into 88,011 contigs (N50: 1056 bp) using Trinity (Grabherr et al., 2011). With the MISA tool (Thiel et al., 2003;  http://pgrc.ipk-gatersleben.de/misa), 11,100 SSRs were detected in 9456 contigs. Of them, dinucleotide repeat motifs (72.73%) were the most common, followed by tri- (24.69%), tetra- (2.23%), penta- (0.19%), and hexanucleotide (0.16%) repeats. Using Primer3 (Rozen and Skaletsky, 1999), 115 paired primers were designed on the basis of randomly selected contigs containing SSR loci, which were deposited in GenBank ( Appendix S1 (apps.1600064_s1.docx)).

A total of 48 individuals of C. bucklandioides representing two populations were used to evaluate the polymorphisms of the target SSR loci, and 28 individuals of M. laosensis, E. tonkinensis, and E. populnea were used to test their transferability (Appendix 1). Total genomic DNA was extracted from silica-dried leaves of these individuals using the modified CTAB method (Doyle, 1987). Voucher specimens of these species were deposited at the Herbarium of Sun Yat-sen University, Guangzhou, Guangdong Province, China.

The PCR amplification trials were performed on two individuals from each of the two C. bucklandioides populations according to Fan et al. (2013), with appropriate annealing temperature (52–55°C; Table 1). For the 59 primer pairs that showed clear peaks with expected allele size, six individuals from each population were selected to tentatively assess their size polymorphism. The products were inspected with the Fragment Analyzer Automated CE System (Advanced Analytical Technologies [AATI], Ames, Iowa, USA) using the Quant-iT PicoGreen dsDNA Reagent Kit (35–500 bp; Invitrogen, Carlsbad, California, USA). The raw data were further processed to obtain allele size and number using PROSize version 2.0 software (AATI). The results showed that 11 loci were polymorphic in C. bucklandioides, and 48 loci were monomorphic. Further PCR amplification was performed on 48 individuals of C. bucklandioides with these 11 polymorphic primer pairs. The statistical parameters, including the number of alleles per locus (A), observed heterozygosity (H_o), and expected heterozygosity (H_e), were calculated with GenAlEx version 6.5 (Peakall and Smouse, 2012). GENEPOP 4.3 was used to measure the departure from Hardy–Weinberg equilibrium (HWE) (Rousset, 2008). The results showed that A varied from two to five, and H_o and H_e ranged from 0.000 to 0.941 and from 0.000 to 0.699, respectively. Four and six loci showed significant deviation from HWE in the Mt. Diaoluo and Mt. Jianfeng populations, respectively (see Table 2).

Table 1.

Characteristics of 19 microsatellite loci isolated from Chunia bucklandioides that showed polymorphism in C. bucklandioides or that could be amplified in closely related taxa.

Table 2.

Amplification and polymorphism of 19 microsatellite loci in populations of the four species.^a

Finally, the cross-amplification of the 59 primers that successfully amplified in C. bucklandioides was also tested in M. laosensis, E. tonkinensis, and E. populnea. Of them, 13 amplified in M. laosensis, and five amplified in E. tonkinensis and E. populnea (Table 2).

CONCLUSIONS

Here, we isolated and characterized a set of 11 polymorphic EST-SSR markers, which may be useful for future conservation genetic studies of C. bucklandioides. The cross-genus amplification and polymorphism were also tested in three related species.