Centromere-Specific Retrotransposons and Very-Long-Chain Fatty Acid Biosynthesis in the Genome of Yellowhorn (Xanthoceras sorbifolium, Sapindaceae), an Oil-Producing Tree With Significant Drought Resistance

In-depth genome characterization is still lacking for most of biofuel crops, especially for centromeres, which play a fundamental role during nuclear division and in the maintenance of genome stability. This study applied long-read sequencing technologies to assemble a highly contiguous genome for yellowhorn (Xanthoceras sorbifolium), an oil-producing tree, and conducted extensive comparative analyses to understand centromere structure and evolution, and fatty acid biosynthesis. We produced a reference-level genome of yellowhorn, ∼470 Mb in length with ∼95% of contigs anchored onto 15 chromosomes. Genome annotation identified 22,049 protein-coding genes and 65.7% of the genome sequence as repetitive elements. Long terminal repeat retrotransposons (LTR-RTs) account for ∼30% of the yellowhorn genome, which is maintained by a moderate birth rate and a low removal rate. We identified the centromeric regions on each chromosome and found enrichment of centromere-specific retrotransposons of LINE1 and Gypsy in these regions, which have evolved recently (∼0.7 MYA). We compared the genomes of three cultivars and found frequent inversions. We analyzed the transcriptomes from different tissues and identified the candidate genes involved in very-long-chain fatty acid biosynthesis and their expression profiles. Collinear block analysis showed that yellowhorn shared the gamma (γ) hexaploidy event with Vitis vinifera but did not undergo any further whole-genome duplication. This study provides excellent genomic resources for understanding centromere structure and evolution and for functional studies in this important oil-producing plant.

Growth, Physiological, and Photosynthetic Responses of Xanthoceras sorbifolium Bunge Seedlings Under Various Degrees of Salinity

Xanthoceras sorbifolium Bunge is priced for its medical and energetic values. The species also plays a key role in stabilizing ecologically fragile areas exposed to excess soil salinity. In this study, the effects of salinity on the growth, physiological, and photosynthetic parameters of X. sorbifolium Bunge were investigated. The X. sorbifolium seedlings were subjected to five salt treatments: 0 (control, CK), 70, 140, 210, and 280 mM of sodium chloride (NaCl) solutions. NaCl caused a decrease in plant height, specific leaf area, biomass, and root parameters. Leaf wilting and shedding and changes in root morphology, such as root length, root surface area, and root tips were observed. This study found that X. sorbifolium is tolerant to high salinity. Compared with the CK group, even if the concentration of NaCl was higher than 210 mM, the increase of the relative conductivity was also slow, while intercellular CO2 concentration had a similar trend. Moreover, NaCl stress caused an increase in the malondialdehyde (MDA), soluble proteins, and proline. Among the enzymes in the plant, the catalase (CAT) activity increases first and decreased with the increase in the intensity of NaCl stress, but the salt treatment had no significant effect on superoxide dismutase (SOD) activity. The peroxidase (POD) showed an increasing trend under salt stress. It was found that the photosynthesis of X. sorbifolium was notably impacted by saline stress. NaCl toxicity induced a noticeable influence on leaf net photosynthetic rate (Pn), stomatal conductance (Gs), intercellular CO2 concentration (Ci), transpiration rate (E), and water use efficiency (Wue). As salt concentration increased, the content of chlorophyll decreased. It can be found that a low concentration of NaCl induced the increase of photosynthetic capacity but a high-intensity exposure to stress resulted in the reduction of photosynthetic efficiency and SOD activity, which had a positive correlation. In summary, salt-induced ionic stress primarily controlled root morphology, osmotic adjustment, and enzyme activities of salt-treated X. sorbifolium leaves, whereas the low salt load could, in fact, promote the growth of roots.

Potential Suitable Habitat of Two Economically Important Forest Trees (Acer truncatum and Xanthoceras sorbifolium) in East Asia under Current and Future Climate Scenarios

Acer truncatum Bunge and Xanthoceras sorbifolium Bunge are small deciduous trees distributed in East Asia and have high ecological and nutrient value due to their strong environmental adaptability and seed oil abundant in nervonic acid and unsaturated fatty acids. However, their natural distribution remains unclear, which will also be affected by the changing climatic conditions. The main purpose of this study was to map and predict the current and future potential suitable habitats of these two species using MaxEnt based on the presence location of species and environmental variables. The results showed that A. truncatum was more suitable for warm and humid climates and was more durable to climate change compared to X. sorbifolium. Under the current environmental conditions, the suitable habitat of A. truncatum was mainly concentrated in Inner Mongolia Plateau, Loess Plateau, Sichuan Basin, Northeast Plain, North China Plain, Korean Peninsula, as well as Japan, with an area of 115.39 × 104 km2. X. sorbifolium was mainly distributed in Inner Mongolia Plateau and Loess Plateau with an area of 146.15 × 104 km2. Under future climate scenarios, the model predicted that higher concentrations of greenhouse gas emissions could result in greater expansion of the potential distribution of both species. Meanwhile, the study also revealed that the two species migrated to the north by east to varying degrees with the change in suitable habitats. This work could provide scientific basis for resource protection and utilization of the two economic forest trees.

Xanthoceras sorbifolium Bunge: A Review on Botany, Phytochemistry, Pharmacology, and Applications

Xanthoceras sorbifolium Bunge (Sapindaceae) is a native Chinese plant with promising applications as a biofuel feedstock and a source of novel drugs. Historical records and documents from different periods have mentioned the use of X. sorbifolium and its botanical constituents in treating diseases, highlighting its central role in Chinese and Mongolian traditional medicinal therapies. Phytochemical research has focused on the husks, leaves, trunks, and branches of this herb. A total of 278 chemical compounds have been isolated and divided into 8 categories: triterpenoids, flavonoids, phenylpropanoids, steroids, phenols, fatty acids, alkaloids, and quinones. Modern pharmacological studies on X. sorbifolium have demonstrated positive effects on learning and memory, as well as anti-inflammatory, anti-tumor, and anti-oxidative properties. This review provides a comprehensive analysis of the available research on X. sorbifolium, focusing on the relationship between chemical constituents, traditional uses, and pharmacological effects. We also assess the potential for therapeutic and other applications of this plant in support of further research and development of X. sorbifolium.

Evaluation of “Genotype x Environment” Interaction for Performance in the Potential Energy Plant Xanthoceras sorbifolium Under Multi-Environment

Xanthoceras sorbifolium Bunge has attracted the attention of the world because of its potential to produce biodiesel. We tested the traits of the seedlings of X. sorbifolium from 26 natural provenances cultivated in three locations of Zhangwu (ZW), Jingbian (JB) and Anqiu (AQ), and analyzed the genotype x environment interaction by BLUP-GGE method. The results showed that the genotype effect, environmental main effect and genotype-environment interaction effect have significant influence on X. sorbifolium growth in the early growth stage, and the variation of ground diameter is greater than that of tree height. The genotypes G25 with the highest yield at the early growth stage, G15 with the highest stable yield, and G9, G12 and G10 with good yield and stable yield were selected. Among them, G12 is a specific high quality genotype for ZW, G10 has the best tree height in JB and AQ, and G9 has the best ground diameter in AQ. This information can evaluate each experimental site and high-quality genotypes, and provide scientific guidance and basis for subsequent biodiesel production of X. sorbifolium.