Transcriptome sequences generated by next-generation sequencing technologies can be utilized to rapidly detect and characterize a large number of gene-based microsatellites from different plants. Rhododendron rex Lévl. is a perennial woody species from the family Ericaceae and an endangered plant with high ornamental value endemic to Southwestern China. Nevertheless, the genetic and genomic information of R. rex remain unknown. In this study, we performed transcriptome sequencing for R. rex leaf samples, and generated large transcript sequences for functional characterization and development gene-associated SSR markers. A total of 164,242 unigenes were assembled and 115,089 (70.07%) unigenes were successfully annotated in public databases. In addition, a total of 15,314 potential EST-SSRs were identified, and the frequency of SSRs in the R. rex unigenes was 9.32%, with an average of one EST-SSR per 5.65 kb. The most abundant type was repeated di-nucleotide (54.63%), followed by mono- (26.03%) and tri-nucleotide (18.51%) repeats. Based on the SSR-containing sequence, 100 primer pairs were randomly selected and synthesized and used for assessment of the polymorphism. Thirty-six primer pairs were polymorphic and revealed polymorphism among 20 individuals from four R. rex populations. A total of 197 alleles were identified, with an average of 5.472 alleles per locus. The Polymorphism Information Content ranged from 0.154 to 0.870, with a mean of 0.482. The newly developed EST-SSR markers exhibited high transferability (58.33%–83.33%) among the six subgenera. Thus, these novel EST-SSR markers developed would provide valuable sequence resources for population structure, genetic diversity analysis, and genetic resource assessments of R. rex and its related species.

Comprehensive studies on the genetic diversity and structure of endangered species are urgently needed to promote effective conservation and management activities. The big tree rhododendron, Rhododendron protistum var. giganteum, is a highly endangered species with only two known endemic populations in a small area in the southern part of Yunnan Province in China. Unfortunately, limited information is available regarding the population genetics of this species. Therefore, we conducted amplified fragment length polymorphism (AFLP) analysis to characterize the genetic diversity and variation of this species within and between remaining populations. Twelve primer combinations of AFLP produced 447 unambiguous and repetitious bands. Among these bands, 298 (66.67 %) were polymorphic. We found high genetic diversity at the species level (percentage of polymorphic loci = 66.67 %, h = 0.240, I = 0.358) and low genetic differentiation (G_st = 0.110) between the two populations. Gene flow between populations (N_m) was relatively high at 4.065. Analysis of molecular variance results revealed that 22 % of the genetic variation was partitioned between populations and 78 % of the genetic variation was within populations. The presence of moderate to high genetic diversity and low genetic differentiation in the two populations can be explained by life history traits, pollen dispersal and high gene flow (N_m = 4.065). Bayesian structure and principal coordinate analysis revealed that 56 sampled trees were clustered into two groups. Our results suggest that some rare and endangered species are able to maintain high levels of genetic diversity even at small population sizes. These results will assist with the design of conservation and management programmes, such as in situ and ex situ conservation, seed collection for germplasm conservation and reintroduction.

Rapid temperature changes in mountain ecosystems pose a great threat to alpine plant species and communities. Rhododendron species, as the major component of alpine and sub-alpine vegetation, have been demonstrated to be sensitive to climate changes. Therefore, understanding how alpine Rhododendron species spread to new habitats and how their geographical distribution range shifts is crucial for predicting their response to global climate change and for facilitating species conservation and reintroduction. In this study, we applied MaxEnt modeling and integrated climate, topography, and soil variables in three periods under three climate change scenarios to predict the suitable habitat for four Rhododendron species in China. We measured the potential distribution change in each species using the change ratio and the direction of centroid shifts. The predicted results showed that (1) the threatened species R. protistum would have a maximum decrease of 85.84% in its distribution range in the 2070s under RCP 8.5, and R. rex subsp. rex as a threatened species would experience a distribution range expansion (6.62–43.10%) under all of the three climate change scenarios in the 2070s. (2) R. praestans would experience a reduction in its distribution range (7.82–28.34%) under all of the three climate change scenarios in the 2070s. (3) The four Rhododendron species would be moved to high latitudes in the north-westward direction as a whole in the future, especially the two threatened species R. protistum and R. rex subsp. rex. (4) Aside from climate variables, soil factors also exert an important influence on the distribution of Rhododendron species. This study revealed the species-specific response of Rhododendron species to climate change. The results can not only provide novel insights into conservation strategies of Rhododendron species, but also propose a valuable method for the habitat selection during the reintroduction of endangered species.

Cinnamomum chago (family Lauraceae) is an essential source of timber and oil. This plant is narrowly distributed in the western part of the Yunnan Province. In this study, the distribution, habitat, and biological characteristics of C. chago were examined through field investigation. The genetic diversity and the variation of the remnant populations were also studied using the inter-simple sequence repeat technique. Results showed that C. chago is mainly distributed in the upstream tributary mountains of Lancang River in Yunlong County of Yunnan Province. The species distribution exhibited a fragmented pattern with five isolated populations and high-frequency anthropogenic interference. A combination of morphological features (opposite leaves, pinnate leaf veins, absence of glandular fossa, large drupe, small punch, and pollen surface with triangular spike grain, with cushion bumps at the base) indicated that C. chago is a key phylogenetic taxon between the two sections of Asian Cinnamomum plants (Sect. Camphora (Trew) Meissn. and Sect. Cinnamomum). Analysis of the genetic diversity of C. chago indicated that it has a moderately high level of genetic diversity at the population and species levels (populations level: N_e = 1.629, H = 0.348, I = 0.504, and PPB = 83.3%; species level: N_e = 1.864, H = 0.460, I = 0.652, and PPB = 100%). Analysis of molecular variance revealed that 17% of the genetic variation was divided between the populations, whereas 83% was observed within the populations. Based on these results, we suggest the inclusion of C. chago in the Wild Plants with Extremely Small Populations in China. Moreover, the species should be given special attention and protection. Some strategies were proposed for the conservation of the C. chago populations.