Taxus yunnanensis genome offers insights into gymnosperm phylogeny and taxol production

Taxol, a natural product derived from Taxus, is one of the most effective natural anticancer drugs and the biosynthetic pathway of Taxol is the basis of heterologous bio-production. Here, we report a high-quality genome assembly and annotation of Taxus yunnanensis based on 10.7 Gb sequences assembled into 12 chromosomes with contig N50 and scaffold N50 of 2.89 Mb and 966.80 Mb, respectively. Phylogenomic analyses show that T. yunnanensis is most closely related to Sequoiadendron giganteum among the sampled taxa, with an estimated divergence time of 133.4−213.0 MYA. As with most gymnosperms, and unlike most angiosperms, there is no evidence of a recent whole-genome duplication in T. yunnanensis. Repetitive sequences, especially long terminal repeat retrotransposons, are prevalent in the T. yunnanensis genome, contributing to its large genome size. We further integrated genomic and transcriptomic data to unveil clusters of genes involved in Taxol synthesis, located on the chromosome 12, while gene families encoding hydroxylase in the Taxol pathway exhibited significant expansion. Our study contributes to the further elucidation of gymnosperm relationships and the Taxol biosynthetic pathway.

Effects of exogenous NO on antioxidant system of Taxus plants under simulated acid rain stress

Taxus is a famous medicinal and landscape tree species. The aim of this study was to explore the effect of exogenous nitric oxide (NO) on the resistance of Taxus plants to acid rain stress and to identify Taxus species with strong acid rain resistance by principal component analysis and comprehensive evaluation. In this study, sodium nitroprusside (SNP) was used as the exogenous NO donor. The effects of different SNP solution concentrations on the antioxidant systems of three Taxus species subjected to simulated acid rain stress (pH = 3.0) were compared. In order to achieve this goal, we determined the rate of O2- production, the ASA and GSH contents in leaves of three Taxus plants (Taxus mairei, Taxus chinensis, and Taxus yunnanensis). At the same time, the active leaves of some antioxidant enzymes (SOD, POD, CAT, APX and GR) were determined. For Taxus chinensis plants subjected to acid rain stress, treatment with an SNP concentration of 0.25 mmol·L-1 led to the most significant improvements in the antioxidant system. For Taxus mairei and Taxus yunnanensis, the treatment with the SNP concentration of 0.50 mmol·L-1 was best for improving their antioxidant systems under stress. Meanwhile, Taxus chinensis had the strongest resistance to simulated acid rain, followed by Taxus mairei and Taxus yunnanensis.

Omic analysis of the endangered Taxaceae species Pseudotaxus chienii revealed the differences in taxol biosynthesis pathway between Pseudotaxus and Taxus yunnanensis trees

Background Taxol is an efficient anticancer drug accumulated in Taxus species. Pseudotaxus chienii is an important member of Taxaceae, however, the level of six taxoids in P. chienii is largely unknown. Results High accumulation of 10-DAB, taxol, and 7-E-PTX suggested that P. chienii is a good taxol-yielding species for large-scale cultivation. By the omics approaches, a total of 3,387 metabolites and 61,146 unigenes were detected and annotated. Compared with a representative Taxus tree (Taxus yunnanensis), most of the differentially accumulated metabolites and differential expressed genes were assigned into 10 primary and secondary metabolism pathways. Comparative analyses revealed the variations in the precursors and intermediate products of taxol biosynthesis between P. chienii and T. yunnanensis. Taxusin-like metabolites highly accumulated in P. chienii, suggesting a wider value of P. chienii in pharmaceutical industry. Conclusions In our study, the occurrence of taxoids in P. chienii was determined. The differential expression of key genes involved in the taxol biosynthesis pathway is the major cause of the differential accumulation of taxoids. Moreover, identification of a number of differentially expressed transcription factors provided more candidate regulators of taxol biosynthesis. Our study may help to reveal the differences between Pseudotaxus and Taxus trees, and promote resource utilization of the endangered and rarely studied P. chienii.

Low genetic diversity in the endangered Taxus yunnanensis following a population bottleneck, a low effective population size and increased inbreeding

Taxus yunnanensis, which is an endangered tree that is considered valuable because it contains the effective natural anticancer metabolite taxol and heteropolysaccharides, has long suffered from severe habitat fragmentation. In this study, the levels of genetic diversity in two populations of 136 individuals were analyzed based on eleven polymorphic microsatellite loci. Our results suggested that these two populations were characterized by low genetic diversity (NE = 2.303/2.557; HO = 0.168/0.142; HE = 0.453/0.517), a population bottleneck, a low effective population size (Ne = 7/9), a high level of inbreeding (FIS = 0.596/0.702), and a weak, but significant spatial genetic structure (Sp = 0.001, b = −0.001*). Habitat fragmentation, seed shadow overlap and limited seed and pollen dispersal and potential selfing may have contributed to the observed gene tic structure. The results of the present study will enable development of practical conservation measures to effectively conserve the valuable genetic resources of this endangered plant.