Genome-wide analysis of the heat shock transcription factor family reveals saline-alkali stress responses in Xanthoceras sorbifolium

The heat shock transcription factor (HSF) family is involved in regulating growth, development, and abiotic stress. The characteristics and biological functions of HSF family member in X. sorbifolium, an important oil and ornamental plant, have never been reported. In this study, 21 XsHSF genes were identified from the genome of X. sorbifolium and named XsHSF1-XsHSF21 based on their chromosomal positions. Those genes were divided into three groups, A, B, and C, containing 12, one, and eight genes, respectively. Among them, 20 XsHSF genes are located on 11 chromosomes. Protein structure analysis suggested that XsHSF proteins were conserved, displaying typical DNA binding domains (DBD) and oligomerization domains (OD). Moreover, HSF proteins within the same group contain specific motifs, such as motif 5 in the HSFC group. All XsHSF genes have one intron in the CDS region, except XsHSF1 which has two introns. Promoter analysis revealed that in addition to defense and stress responsiveness elements, some promoters also contained a MYB binding site and elements involved in multiple hormones responsiveness and anaerobic induction. Duplication analysis revealed that XsHSF1 and XsHSF4 genes were segmentally duplicated while XsHSF2, XsHSF9, and XsHSF13 genes might have arisen from transposition. Expression pattern analysis of leaves and roots following salt-alkali treatment using qRT-PCR indicated that five XsHSF genes were upregulated and one XsHSF gene was downregulated in leaves upon NaCl treatment suggesting these genes may play important roles in salt response. Additionally, the expression levels of most XsHSFs were decreased in leaves and roots following alkali-induced stress, indicating that those XsHSFs may function as negative regulators in alkali tolerance. MicroRNA target site prediction indicated that 16 of the XsHSF genes may be regulated by multiple microRNAs, for example XsHSF2 might be regulated by miR156, miR394, miR395, miR408, miR7129, and miR854. And miR164 may effect the mRNA levels of XsHSF3 and XsHSF17, XsHSF9 gene may be regulated by miR172. The expression trends of miR172 and miR164 in leaves and roots on salt treatments were opposite to the expression trend of XsHSF9 and XsHSF3 genes, respectively. Promoter analysis showed that XsHSFs might be involved in light and hormone responses, plant development, as well as abiotic stress responses. Our results thus provide an overview of the HSF family in X. sorbifolium and lay a foundation for future functional studies to reveal its roles in saline-alkali response.

The relationship between canopy microclimate, fruit and seed yield, and quality in Xanthoceras sorbifolium

Xanthoceras sorbifolium has high oil content and important biomass energy value, but its development is limited by the problem of low yield. This study investigated the relationship between the canopy microclimate, fruit yield, and fruit quality of Xanthoceras sorbifolium. Difference between the distributions of canopy microclimate factors as well as fruit and seed parameters in the inner and outer canopies of the lower layer, as well as between the inner and outer canopies of the upper layer, were investigated for a period of one year. Canopy structure induced significant differences between canopy microclimate factors during various periods of the year. Light intensity and temperature of the outer and upper canopies were higher than those of inner and lower canopies. However, relative humidity showed an opposing trend. Light intensity was significantly and positively correlated with fruit set percentage, fruit yield, and seed yield. Temperature was significantly and positively correlated with fruit yield and seed yield, but significantly negatively correlated with the oil concentration of seed kernels. Fruit and seed yields significantly decreased from the outer to the inner canopy and from the upper to the lower canopy. Fruit set percentage in the outer canopy was also significantly higher than that in the inner canopy. However, oil concentrations in the seed kernels of the lower layer were significantly higher than those of the upper layer. Additionally, regression analysis was used to construct evaluation models for microclimate, fruit, and seed parameters. Regression equations corresponding to the association between single microclimatic factors during different periods and the fruit and seed parameters may provide a reference for canopy pruning and help develop an optimal regression model that may be used to predict and estimate fruit and seed parameters.

A naturally-occurring phenomenon of flower color change during flower development in Xanthoceras sorbifolium

Xanthoceras sorbifolium (yellowhorn) is originated in China and is a unique tree in northern China. Yellowhorn is very popular because of the gradual color change of its flower at different flower developmental stages. During flowering development, the color at the base of yellowhorn flower petals gradually changes from yellow to purple. The mechanism of this miraculous phenomenon is still unclear. Here we show that anthocyanin accumulation during flowering development is the main reason for this color change. RT-PCR results show that the expression level of a variety of anthocyanin biosynthesis genes changes in different flower developmental stages. Realtime results show that the expression changes of these anthocyanin biosynthesis genes are positively regulated by a cluster of R2R3-MYB transcription factor genes, XsMYB113s. Furthermore, the DNA methylation analysis showed that CHH methylation status on the transposon element near the XsMYB113-1 influence its transcript level during flowering development. Our results suggest that dynamic epigenetic regulation of the XsMYB113-1 leads to the accumulation of anthocyanins during yellowhorn flower color change. These findings reemphasize the role of epigenetic regulation in flower development and provide a foundation for further studies of epigenetic regulation in long-lived woody perennials.

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.

Natural therapeutic agents for neurodegenerative diseases from the shells of Xanthoceras sorbifolium

Neuroinflammation is linked to neurodegenerative diseases, manifested by the microglial-released over-production of nitric oxide (NO). However, so far there is no effective strategy regarding curing or preventing neurodegenerative diseases. Triterpene saponins from Xanthoceras sorbifolium were proved to be capable of eliciting a protective effect in neurodegenerative diseases. Thus, a systematic chemical study on the 70% ethanol extract of X. sorbifolium was conducted, leading to the identification of 22 compounds, including four previously undescribed triterpenes saponins and 14 known ones, along with four alkaloids. Their structures were elucidated by physicochemical and spectral methods. The in vivo anti-AD effects of 1-18 were predicted with a field-based 3D-QSAR model and anti-neuroinflammatory activities were assayed in BV-2 cells by assessing LPS-induced NO production and examine levels of iNOS, TNF-α, IL-1β, and IL-6 to support the predicted results. As a result, compounds 14, 16, 19, and 20 could have therapeutic potentials for neurodegenerative diseases due to their potent anti-neuroinflammatory activities.

Chemical constituents from shells of Xanthoceras sorbifolium

Three undescribed triterpenes and four previously unreported saponins, along with two known ones, were isolated from shells of Xanthoceras sorbifolium (Sapindaceae). Their structures were elucidated by the interpretation of 1D and 2D NMR data. The nitric oxide (NO) assay revealed that 28-O-isobutyryl-21-O-angeloyl-R₁-barrigenol and 3-O-β-D-6-O-methylglucuronopyranosyl-21,22-di-O-angeloyl-R₁-barrigenol possessed stronger inhibitory effects on LPS-induced NO overproduction (IC₅₀ = 18.5 ± 1.2 and 28.2 ± 1.8 μM, respectively) than the positive drug minocycline (IC₅₀ = 30.1 ± 1.3 μM) in activated BV2 cells. Western blot, RT-qPCR, and docking experiments further validated that the regulation of iNOS and IL-1β expressions was involved in the anti-neuroinflammatory effects of these two compounds.

In vivo evaluation and atom-based 3D-QSAR studies on saponins from shells of Xanthoceras sorbifolium Bunge as anti-AD agents

A series of oleanane type of glycosides (1-19), including nine undescribed ones (1-9), were isolated and identified from Xanthoceras sorbifolium. Subsequently, an atom-based 3D-QSAR model was constructed based on results of the in vivo anti-AD evaluation of the isolates (2-3, 10-17) and nine literature-reported anti-AD oleanane type of glycosides to clarify the structure-anti-AD activity, and under the guidance of which 19 was predicted and proved to elicit a nearly equivalent in vivo anti-AD effect as xanthoceraside and donepezil that were used as positive drugs in the Y maze and Morris water maze test.

Conservation of genetic diversity hotspots of the high-valued relic yellowhorn (Xanthoceras sorbifolium) considering climate change predictions

Genetic structure and major climate factors may contribute to the distribution of genetic diversity of a highly valued oil tree species Xanthoceras sorbifolium (yellowhorn). Long-term over utilization along with climate change is affecting the viability of yellowhorn wild populations. To preserve the species known and unknown valuable gene pools, the identification of genetic diversity "hotspots" is a prerequisite for their consideration as in situ conservation high priority. Chloroplast DNA (cpDNA) diversity was high among 38 natural populations (H d = 0.717, K = 4.616, Tajmas' D = -0.22) and characterized by high genetic divergence (F ST = 0.765) and relatively low gene flow (N m = 0.03), indicating populations isolation reflecting the species' habitat fragmentation and inbreeding depression. Six out of the studied 38 populations are defined as genetic diversity "hotspots." The number and geographic direction of cpDNA mutation steps supported the species southwest to northeast migration history. Climatic factors such as extreme minimum temperature over 30 years indicated that the identified genetic "hotspots" are expected to experience 5°C temperature increase in next following 50 years. The results identified vulnerable genetic diversity "hotspots" and provided fundamental information for the species' future conservation and breeding activities under the anticipated climate change. More specifically, the role of breeding as a component of a gene resource management strategy aimed at fulfilling both utilization and conservation goals.

The superoxide dismutase genes might be required for appropriate development of the ovule after fertilization in Xanthoceras sorbifolium

Superoxide dismutase genes were expressed differentially along with developmental stages of fertilized ovules in Xanthoceras sorbifolium, and the XsMSD gene silencing resulted in the arrest of fertilized ovule development. A very small percentage of mature fruits (ca. 5%) are produced relative to the number of bisexual flowers in Xanthoceras sorbifolium because seeds and fruits are aborted at early stages of development after pollination. Reactive oxygen species (ROS) in plants are implicated in an extensive range of biological processes, such as programmed cell death and senescence. Superoxide dismutase (SOD) activity might be required to regulate ROS homeostasis in the fertilized ovules of X. sorbifolium. The present study identified five SOD genes and one SOD copper chaperone gene in the tree. Their transcripts were differentially expressed along different stages of fertilized ovule development. These genes showed maximum expression in the ovules at 3 days after pollination (DAP), a time point in which free nuclear endosperm and nucleus tissues rapidly develop. The XsCSD1, XsFSD1 and XsMSD contained seven, eight, and five introns, respectively. Analysis of the 5'-flanking region of XsFSD1 and XsMSD revealed many cis-acting regulatory elements. Evaluation of XsMSD gene function based on virus-induced gene silencing (VIGS) indicated that the gene was closely related to early development of the fertilized ovules and fruits. This study suggested that SOD genes might be closely associated with the fate of ovule development (aborted or viable) after fertilization in X. sorbifolium.