High genetic diversity in Taihangia rupestris Yu et Li, a rare cliff herb endemic to China, based on inter-simple sequence repeat markers
Highlights
► Relatively high genetic diversity was detected at the species level. ► Most of the variation occurred within the population. ► Geographical distance was significantly correlated with genetic distance. ► Ancient origin and mixed reproductive modes leaded to its high genetic diversity.
Introduction
Taihangia rupestris Yu et Li was originally found in 1974 and was formally described in 1980 as the only species of the Taihangia belonging to the family Rosaceae (Yu and Li, 1980). T. rupestris is an endangered perennial herb endemic to China, and its distribution is restricted to the eastern edge of the Taihang Mountains, from northern latitude 35°22′ to 36°51′ and from eastern longitude 113°15′ to 113°50′ (Shen et al., 1994). T. rupestris plants grow mostly in small crevices on the faces of shaded cliffs at altitudes ranging from 600 to 1500 m a.s.l., especially on vertical cliffs with a “U” shape, where direct sunshine cannot be received (Yu and Li, 1983, Shen et al., 1994, Lu et al., 1995). T. rupestris is self-compatible and can reproduce both sexually and asexually (Lu et al., 1995). In the field, because of its weak sexual reproduction, T. rupestris expands populations mainly by asexual reproduction (Lu et al., 1995), and most of present individuals come from ancestral clones (Tang, 2004). According to its morphology, anatomy of carpel, chromosome counting, and microscopic structure of pollen, T. rupestris is the most primitive diploid species (2n = l4) in the tribe Dryadeae in the family Rosaceae, so it is an ancient relic species (Yu and Li, 1983). T. rupestris has three important attributes: first, because it evolved from a bisexual flower to a unisexual flower, T. rupestris is at an important systematic position in the tribe Dryadeae, and studying it could reveal new insights in the evolution of the tribe Dryadeae (Yu and Li, 1983); second, this species is a valuable wild flower resource in the early springtime. It has white flowers, with a diameter of 3–4.5 cm, that bloom on the vertical cliffs in March and has been named the “rare cliff flower” in the Taihang mountains (Xu et al., 2006); finally, T. rupestris, which contains β-sitosterol, ursolic acid, allic acid, glucopyranoside, and other potentially bioactive compounds, is a medicinal herb that has been reported to cure tinea (Zhang et al., 1994, Wang and Wen, 2001).
Due to its narrow range of distribution and its special habitat, the number and size of T. rupestris populations has steadily decreased due to climate change and vegetation destruction (Tang, 2004). Now the species is at risk of extinction and has been listed as a national second-class protection plant of China (Wang and Xie, 2004). T. rupestris individuals have previously been found at some locations, such as Yidoushui, Huanghua, Jindengshan, Lianggou, Shenjiaogou, Huangbeijiao, Shaoyuan, Chafang, Xiaoyuegou and Huangpozhang (Yu and Li, 1980, Song et al., 1989, Shen et al., 1994, Song and Qu, 1996), but Tang (2004) found no individuals of T. rupestris in Jiyuan (Huangbeijiao, Shaoyuan, Chafang) and Qinyang (Xiaoyuegou, Huangpozhang) in her two field surveys. Furthermore, in our recent surveys, we could not find T. rupestris individuals in Shenjiaogou. Given this serious situation, suitable protection strategies for T. rupestris should be urgently implemented.
Molecular markers are useful tools in conservation genetic studies (Frankham et al., 2002). Inter-simple sequence repeat (ISSR) is a molecular marker targeting simple sequence repeats (SSR), by which the length variation of a DNA fragment between adjacent microsatellites is detected in the entire genome. ISSR has an advantage over randomly amplified polymorphic DNA (RAPD) because its primers are longer, allowing for higher annealing temperatures that apparently provide a higher reproducibility of fragments than RAPD (Wolfe and Liston, 1998). Because of its simple technology and its high level of polymorphism, ISSR has been widely used for population genetic studies (Clausing et al., 2001, Archibald et al., 2006, Li and Jin, 2008, George et al., 2009, Zhou et al., 2009).
Population genetics data can provide valuable information, often unattainable via other approaches, for monitoring species of management, conservation and ecological interest (Schwartz et al., 2006). In the present study, ISSR markers were employed to investigate the genetic diversity and genetic differentiation of T. rupestris. The main objectives of the study were to (a) characterize the level of genetic diversity in this endemic cliff species, (b) reveal the pattern of genetic differentiation among populations and (c) assess feasible approaches for T. rupestris conservation.
Section snippets
Plant materials
During two field surveys in 2008 and 2009, we collected leaf samples from 220 individuals representing 10 extant populations of T. rupestris throughout the entire geographical range of species (Fig. 1, Table 1). Within each population, samples were collected from different crevices in order to avoid sampling the same clonal individual. Because of the difficulty of accessing the top and middle parts of vertical cliffs, leaves were sampled from the plants at the bottom of the cliffs. Fresh leaves
Genetic diversity of T. rupestris
Amplification of the ISSR fragments in 220 individuals sampled with 12 primers generated 184 clearly identifiable bands, with a mean of 15.33 bands per primer (Table 2). In all, there were 148 polymorphic bands; the percentage of polymorphic band (PPB) was 47.01% on average at the population level, ranging from 40.22% (LHP) to 53.8% (DPB), and 80.43% at the species level (Table 1). Nei’s gene diversity (h) was estimated to be 0.1865 on average at the population level and 0.2479 at the species
Genetic diversity in T. rupestris
Many studies have demonstrated that endemic and endangered species tend to have a low level of genetic diversity (Torres-Diaz et al., 2007). For example, Cathaya argyrophylla Chun et Kuang occurs currently in widely separated subtropical areas in southern China, and the species-wide nucleotide diversity is the lowest among studied conifers (Wang and Ge, 2006). Saruma henryi Oliv is an endangered perennial herb endemic to middle China, and the genetic diversity is quite low at the population
Acknowledgments
We thank Shi-Xin Zhu, Chun-Feng Li, Li Meng and De-Gui Wei for help with the field survey and sample collection. This study was supported by the Start-up Research Funds for Young Doctors from Henan Agricultural University (30400246).
References (49)
- et al.
Genetic diversity of wild populations of Rheum tanguticum endemic to China as revealed by ISSR analysis
Biochem. Syst. Ecol.
(2010) - et al.
Genetic diversity and relationship of endangered plant Magnolia officinalis (Magnoliaceae) assessed with ISSR polymorphisms
Bioch. Syst. Ecol.
(2011) - et al.
The utility of automated analysis of inter-simple sequence repeat (ISSR) loci for resolving relationships in the Canary Island species of Tolpis (Asteraceae)
Am. J. Bot.
(2006) - et al.
Genetic diversity and structure of the narrow endemic Wyethia reticulata and its congener W. bolanderi (Asteraceae) using RAPD and allozyme techniques
Am. J. Bot.
(1999) - et al.
High levels of genetic structuring as a result of population fragmentation in the tropical tree species Caesalpinia echinata Lam
Biodivers. Conserv
(2005) - et al.
Genetic variation in three endangered species of Encholirium (Bromeliaceae) from Cadeia do Espinhaço, Brazil, selected using RAPD Markers
Biodivers. Conserv
(2006) - et al.
Historical biogeography in a linear system: genetic variation of Sea Rocket (Cakile maritima) and Sea Holly (Eryngium maritimum) along European coasts
Mol. Ecol.
(2001) - et al.
A rapid DNA isolation procedure for small quantities of fresh leaf tissue
Phytochem. Bull.
(1987) - et al.
Detecting the number of clusters of individuals using the software STRUCTURE: a simulation study
Mol. Ecol.
(2005) - et al.
Analysis of molecular variance inferred from metric distances among DNA haplotypes: application to human mitochondrial DNA restriction data
Genetics
(1992)