Beiwei Hou

Comparative Chloroplast Genomes of Photosynthetic Orchids: Insights into Evolution of the Orchidaceae and Development of Molecular Markers for Phylogenetic Applications

The orchid family Orchidaceae is one of the largest angiosperm families, including many species of important economic value. While chloroplast genomes are very informative for systematics and species identification, there is very limited information available on chloroplast genomes in the Orchidaceae. Here, we report the complete chloroplast genomes of the medicinal plant Dendrobium officinale and the ornamental orchid Cypripedium macranthos, demonstrating their gene content and order and potential RNA editing sites. The chloroplast genomes of the above two species and five known photosynthetic orchids showed similarities in structure as well as gene order and content, but differences in the organization of the inverted repeat/small single-copy junction and ndh genes. The organization of the inverted repeat/small single-copy junctions in the chloroplast genomes of these orchids was classified into four types; we propose that inverted repeats flanking the small single-copy region underwent expansion or contraction among Orchidaceae. The AT-rich regions of the ycf1 gene in orchids could be linked to the recombination of inverted repeat/small single-copy junctions. Relative species in orchids displayed similar patterns of variation in ndh gene contents. Furthermore, fifteen highly divergent protein-coding genes were identified, which are useful for phylogenetic analyses in orchids. To test the efficiency of these genes serving as markers in phylogenetic analyses, coding regions of four genes (accD, ccsA, matK, and ycf1) were used as a case study to construct phylogenetic trees in the subfamily Epidendroideae. High support was obtained for placement of previously unlocated subtribes Collabiinae and Dendrobiinae in the subfamily Epidendroideae. Our findings expand understanding of the diversity of orchid chloroplast genomes and provide a reference for study of the molecular systematics of this family.

Iteration expansion and regional evolution: phylogeography of Dendrobium officinale and four related taxa in southern China

The genus Dendrobium was used as a case study to elucidate the evolutionary history of Orchidaceae in the Sino-Japanese Floristic Region (SJFR) and Southeast Asia region. These evolutionary histories remain largely unknown, including the temporal and spatial distribution of the evolutionary events. The present study used nuclear and plastid DNA to determine the phylogeography of Dendrobium officinale and four closely related taxa. Plastid DNA haplotype and nuclear data were shown to be discordant, suggesting reticulate evolution drove the species’ diversification. Rapid radiation and genetic drift appeared to drive the evolution of D. tosaense and D. flexicaule, whereas introgression or hybridization might have been involved in the evolution of D. scoriarum and D. shixingense. The phylogeographical structure of D. officinale revealed that core natural distribution regions might have served as its glacial refuges. In recent years, human disturbances caused its artificial migration and population extinction. The five taxa may have originated from the Nanling Mountains and the Yungui Plateau and then migrated northward or eastward. After the initial iteration expansion, D. officinale populations appeared to experience the regional evolutionary patterns in different regions and follow the sequential or rapid decline in gene exchange.

Phylogeography of the endangered orchid Dendrobium moniliforme in East Asia inferred from chloroplast DNA sequences

Abstract The aim of the current study was to elucidate the phylogeographic history of Dendrobium moniliforme, an endangered orchid species, based on two chloroplast DNA (cpDNA) markers (trnC-petN and trnE-trnT). One hundred and thirty-five samples were collected from 18 natural populations of D. moniliforme covering the entire range of the Sino-Japanese Floristic Region (SJFR) of East Asia. A total of 35 distinct cpDNA haplotypes were identified in these populations, of which 23 haplotypes were each present in only one sample and thus restricted to a single population. The significantly larger NST value (0.586) than GST (0.328) (p < 0.05) demonstrated the presence of strong phylogeographic structure. Phylogenetic analyses indicated that all haplotypes were clustered into two lineages. The genetic diversity of D. moniliforme was high at the species level, reflected in its haplotype diversity (Hd=0.8862), nucleotide diversity (Pi=0.00361), total genetic diversity (HT=0.9011), and significant differentiation (ΦST=0.5482). Based on mismatch distribution analysis and neutrality tests, population expansion was evident in all sampled populations and also in all populations sampled in mainland China. Three refuge areas were identified, one each in southwestern China, central-southeastern China, and the CKJ (Taiwan, Japan and Korea) Islands. The results supported the hypothesis that glacial refugia were maintained on different spatial-temporal scales in the SJFR during the last glacial maximum or earlier cold periods, suggesting that Quaternary refugial isolation promoted allopatric speciation of D. moniliforme in East Asia.

Different evolutionary processes in shaping the genetic composition of Dendrobium nobile in southwest China.

Knowledge of population genetic structure and intrapopulation genetic variation is important for understanding population dynamics and evolutionary processes. Dendrobium nobile is an endangered traditional Chinese tonic medicine. In order to analyze the population differentiation and genetic diversity in D. nobile and propose proper conservation measurements, we genotyped 102 individual plants from 7 natural populations distributed across southwest China at 9 microsatellite loci. Seven pairs of genomic SSR primers were newly designed, and two pairs were chosen from the EST-SSRs. According to the results, the genetic process of D. nobile on Hainan Island and the Chinese mainland might be affected by different evolutionary processes, the genetic drift caused by founder effect has played an important role in shaping the genetic constitution of the Island population. The population of D. nobile in Hainan Island was highly differentiated and displayed low levels of genetic diversity. For the conservation management plans of D. nobile, we propose that individuals in Hainan Island with rare alleles need to be conserved with top priority, and those individuals with rare alleles and the most common alleles also should be concerned. The seven new microsatellite loci may be informative for further evaluation and conservation of the genetic diversity of D. nobile.