Eucommia ulmoides, also called hardy rubber tree, is an economically important tree; however, the lack of its genome sequence restricts the fundamental biological research and applied studies of this plant species. Here, we present a high-quality assembly of its ∼1.2-Gb genome (scaffold N50 = 1.88 Mb) with at least 26 723 predicted genes for E. ulmoides, the first sequenced genome of the order Garryales, which was obtained using an integrated strategy combining Illumina sequencing, PacBio sequencing, and BioNano mapping. As a sister taxon to lamiids and campanulids, E. ulmoides underwent an ancient genome triplication shared by core eudicots but no further whole-genome duplication in the last ∼125 million years. E. ulmoides exhibits high expression levels and/or gene number expansion for multiple genes involved in stress responses and the biosynthesis of secondary metabolites, which may account for its considerable environmental adaptability. In contrast to the rubber tree (Hevea brasiliensis), which produces cis-polyisoprene, E. ulmoides has evolved to synthesize long-chain trans-polyisoprene via farnesyl diphosphate synthases (FPSs). Moreover, FPS and rubber elongation factor/small rubber particle protein gene families were expanded independently from the H. brasiliensis lineage. These results provide new insights into the biology of E. ulmoides and the origin of polyisoprene biosynthesis.

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The study deals with the spatio-temporal distribution of heavy metals in the sediments of Chagan lake, Northeast China. The pollution history of heavy metals is studied simultaneously through the 210Pb dating method by analyzing the characteristic of As, Hg, Cd, Cr, Ni, Cu, Pb, and Zn concentration-depth profiles. The potential ecological risk index (RI) and geo-accumulation index (Igeo) were used to evaluate the contamination degree. Principal component analysis (PCA), based on the logarithmic transformation and isometric log-ratio (ilr) transformed data, was applied with the aim of identifying the sources of heavy metals. The element concentrations show that the heavy metals are enriched in the surface sediment and sediment core with a varying degree, which is higher in the surficial residue. The results of Igeo indicate that the Cd and Hg in the surface sediment have reached a slightly contaminated level while other elements, uncontaminated. The results of RI show that the study area can be classified as an area with moderate ecological risk in which Cd and Hg mostly contribute to the overall risk. For the sediment core, the 210Pb dating results accurately reflect the sedimentary history over 153 years. From two evaluation indices (RI and Igeo) calculated by element concentration, there is no contamination, and the potential ecological risk is low during this period. The comparative study between raw and ilr transformed data shows that the closure effect of the raw data can be eliminated by ilr transformation. After that, the components obtained by robust principal component analysis (RPCA) are more representative than those obtained by PCA, both based on ilr transformed dataset, after eliminating the influence of outliers. Based on ilr transformed data with RPCA, three primary sources could be inferred: Cr, Ni, As, Zn, and Cu are mainly derived from natural sources; the main source of Cd and Hg are associated with agricultural activities and energy development; as for Pb, it originated from traffic and coal-burning activities, which is consistent with the fact that the development of tourism, fishery, and agriculture industries has led to the continuous increasing levels of anthropogenic Pb in Chagan Lake. The summarized results and conclusions will undoubtedly enhance the governmental awareness of heavy metal pollution and facilitate appropriate pollution control measures in Chagan Lake.

4-Coumarate: coenzyme A ligase (4CL) is an important rate-limiting enzyme in phenylpropanoid metabolism that plays an important role in the biosynthesis of phenylpropanoid, flavonoid, lignin and other secondary metabolites in plants. However, the family members and functions have not been identified in Eucommia ulmoides (E. ulmoides). In this study, 35 Eu4CLs were identified in the E. ulmoides genome, and the gene structure, conserved domain, evolutionary relationship and expression pattern were comprehensively analyzed. The results show that 35 Eu4CLs were assembled into three subgroups according to the classification in Arabidopsis, where Eu4CLs in the same subgroup had similar gene structures and conserved protein motifs. Putative cis-element analysis of Eu4CL promoter regions uncovered numerous elements related to the response of stress and plant hormones. Expression patterns showed that Eu4CL4/5/13/34 expression levels were positively related to chlorogenic acid content in different periods, which indicate that the synthesis of chlorogenic acid in E. ulmoides was regulated by multiple genes, and the genes regulating the synthesis of chlorogenic acid in different tissues were different. In addition, nine selected Eu4CL genes showed different expression patterns under cold, WeJA (methyl jasmonate), and ethylene by quantitative reverse transcription-PCR (qRT-PCR) assay, suggesting that Eu4CL genes not only play an important role in the synthesis of chlorogenic acid, but also plays an important role in the process of biotic and abiotic stress. Taken together, these findings provide theoretical reference for further exploring the molecular characteristics and biological functions of Eu4CL genes.