Large-scale advances in SSR markers with high-throughput sequencing in Euphorbia fischeriana Steud

Comparative Transcriptomics and Metabolites Analysis of Two Closely Related Euphorbia Species Reveal Environmental Adaptation Mechanism and Active Ingredients Difference

Roots of Euphorbia fischeriana and Euphorbia ebracteolata are recorded as the source plant of traditional Chinese medicine "Langdu," containing active ingredients with anticancer and anti-AIDS activity. However, the two species have specific patterns in the graphic distribution. Compared with E. ehracteolata, E. fischeriana distributes in higher latitude and lower temperature areas and might have experienced cold stress adaptation. To reveal the molecular mechanism of environmental adaptation, RNA-seq was performed toward the roots, stems, and leaves of E. fischeriana and E. ehracteolata. A total of 6,830 pairs of putative orthologs between the two species were identified. Estimations of non-synonymous or synonymous substitution rate ratios for these orthologs indicated that 533 of the pairs may be under positive selection (Ka/Ks > 0.5). Functional enrichment analysis revealed that significant proportions of the orthologs were in the TCA cycle, fructose and mannose metabolism, starch and sucrose metabolism, fatty acid biosynthesis, and terpenoid biosynthesis providing insights into how the two closely related Euphorbia species adapted differentially to extreme environments. Consistent with the transcriptome, a higher content of soluble sugars and proline was obtained in E. fischeriana, reflecting the adaptation of plants to different environments. Additionally, 5 primary or secondary metabolites were screened as the biomarkers to distinguish the two species. Determination of 4 diterpenoids was established and performed, showing jolkinolide B as a representative component in E. fischeriana, whereas ingenol endemic to E. ebracteolate. To better study population genetics, EST-SSR markers were generated and tested in 9 species of Euphorbia. A total of 33 of the 68 pairs were screened out for producing clear fragments in at least four species, which will furthermore facilitate the studies on the genetic improvement and phylogenetics of this rapidly adapting taxon. In this study, transcriptome and metabolome analyses revealed the evolution of genes related to cold stress tolerance, biosynthesis of TCA cycle, soluble sugars, fatty acids, and amino acids, consistent with the molecular strategy that genotypes adapting to environment. The key active ingredients of the two species were quantitatively analyzed to reveal the difference in pharmacodynamic substance basis and molecular mechanism, providing insights into rational crude drug use.

EST-SSR Primer Development and Genetic Structure Analysis of Psathyrostachys juncea Nevski

Psathyrostachys juncea is a perennial forage grass which plays an important role in soil and water conservation and ecological maintenance in cold and dry areas of temperate regions. In P. juncea, a variety of biotic and abiotic stress related genes have been used in crop improvement, indicating its agronomic, economic, forage, and breeding value. To date, there have been few studies on the genetic structure of P. juncea. Here, the genetic diversity and population structure of P. juncea were analyzed by EST-SSR molecular markers to evaluate the genetic differentiation related to tillering traits in P. juncea germplasm resources. The results showed that 400 simple sequence repeat (SSR) loci were detected in 2,020 differentially expressed tillering related genes. A total of 344 scored bands were amplified using 103 primer pairs, out of which 308 (89.53%) were polymorphic. The Nei's gene diversity of 480 individuals was between 0.092 and 0.449, and the genetic similarity coefficient was between 0.5008 and 0.9111, with an average of 0.6618. Analysis of molecular variance analysis showed that 93% of the variance was due to differences within the population, and the remaining 7% was due to differences among populations. Psathyrostachys juncea materials were clustered into five groups based on population genetic structure, principal coordinate analysis and unweighted pair-group method with arithmetic means (UPGMA) analysis. The results were similar between clustering methods, but a few individual plants were distributed differently by the three models. The clustering results, gene diversity and genetic similarity coefficients showed that the overall genetic relationship of P. juncea individuals was relatively close. A Mantel test, UPGMA and structural analysis also showed a significant correlation between genetic relationship and geographical distribution. These results provide references for future breeding programs, genetic improvement and core germplasm collection of P. juncea.