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Background Vernicia montana and V . fordii are economically important woody oil species in the Euphorbiaceae that have great industrial oil and ornamental greening properties, however, the wild resources of Vernicia trees have been reduced because of their habitat destruction. Considering the diverse economic and ecological importance of Vernicia species, it is important to collect more molecular data to determine the genetic differences between V. montana and V. fordii . Results We sequenced, assembled, and annotated the complete chloroplast (CP) genome of two tung trees based on the genome skimming approach. The whole CP genomes of V. montana and V. fordii were 163,518 bp and 161,495 bp in length, both including a pair of inverted repeats separated by a large single-copy and a small single-copy region. We detected a total number of 311 tandem repeats, 100 dispersed repeats, and 255 simple repeats from V. montana and V. fordii CP genomes. The mean value of nucleotide diversity between the two species was 0.0122, and the average Ka/Ks ratio across all coding genes was 0.3483. Comparative chloroplast genome analysis showed that the coding regions were more conserved than the non-coding regions. The phylogenetic relationships yielded by the complete genome sequences showed that V. montana was closely related to V. fordii and is considered as a sister group. Conclusions We sequenced, assembled, annotated, and analyzed the CP genome of two tung trees, which will be useful in investigating the conservation genetics and potential breeding applications of this oil shrub.

Tung oil tree (Vernicia fordii) is a promising industrial oil crop; however, this tree is highly susceptible to Fusarium wilt disease. Conversely, Vernicia montana is resistant to the pathogen. The APETALA2/ethylene-responsive element binding factor (AP2/ERF) transcription factor superfamily has been reported to play a significant role in resistance to Fusarium oxysporum. In this study, comprehensive analysis identified 75 and 81 putative Vf/VmAP2/ERF transcription factor-encoding genes in V. fordii and V. montana, respectively, which were divided into AP2, ERF, related to ABI3 and VP1 (RAV) and Soloist families. After F. oxysporum infection, a majority of AP2/ERF superfamily genes showed strong patterns of repression in both V. fordii and V. montana. We then identified 53 pairs of one-to-one orthologs in V. fordii and V. montana, with most pairs of orthologous genes exhibiting similar expression in response to the pathogen. Further investigation of Vf/VmAP2/ERF gene expression in plant tissues indicated that the pairs of genes with different expression patterns in response to F. oxysporum tended to exhibit different tissue profiles in the two species. In addition, VmAP2/ERF036, showing the strongest interactions with 666 genes, was identified as a core hub gene mediating resistance. Moreover, qRT-PCR results indicated VmAP2/ERF036 showed repressed expression while its orthologous gene VfAP2/ERF036 had the opposite expression pattern during pathogen infection. Overall, comparative analysis of the Vf/VmAP2/ERF superfamily and indication of a potential hub resistance gene in resistant and susceptible Vernicia species provides valuable information for understanding the molecular basis and selection of essential functional genes for V. fordii genetic engineering to control Fusarium wilt disease.

Vernicia fordii (tung oil tree) is famous in the world for its production of tung oil. Unfortunately, it was infected by the soil-borne fungus Fusarium oxysporum f. sp. fordii 1 (Fof-1) and suffered serious wilt disease. Conversely, its sister species V. montana is highly resistant to Fof-1. The MYB (v-myb myeloblastosis viral oncogene homolog) transcription factors were activated during the pathogen Fof-1 infection according to our previous comparative transcriptomic results. Depending on whether the sequence has a complete MYB-DNA-binding domain, a total of 75 VfMYB and 77 VmMYB genes were identified in susceptible V. fordii and resistant V. montana, respectively. In addition, we detected 49 pairs of one-to-one orthologous Vf/VmMYB genes with the reciprocal-best BLAST-hits (RBH)method. In order to investigate the expression modes and the internal network of MYB transcription factors in the two species responding to Fusarium wilt disease, the expressions of Vf/VmMYBs were then investigated and we found that most orthologous Vf/VmMYB genes exhibited similar expression patterns during the Fof-1 infection. However, four pairs of Vf/VmMYB genes, annotated as unknown proteins and mediator of root architecture, demonstrated absolute opposite expression patterns in the two Vernicia species responding to Fof-1. The interaction network of VmMYB genes were further constructed using weighted gene co-expression network analysis (WGCNA) method and four hub genes showing extremely high interaction with the other 1157 genes were identified. RT-qPCR result verified the opposite expression pattern of the hub gene VmMYB011 and VmMYB041 in two Vernicia species. In summary, co-expression network of the Vf/VmMYBs and significantly opposite related pairs of genes in resistant and susceptible Vernicia species provided knowledge for understanding the molecular basis of Vernicia responding to Fusarium wilt disease.

Rubber wood often exhibits dimensional instability during use, which seriously hinders its widespread application. In order to enhance the dimensional stability of rubber wood, a two-step method was employed in this study to modify rubber wood using two plant-derived compounds, namely sucrose and tung oil. Samples treated alone with sucrose or tung oil were also prepared. The water absorption, dimensional stability, and thermal stability of modified and untreated wood were evaluated. The results show that wood samples treated with 30% sucrose and tung oil had excellent water resistance and dimensional stability based on the synergistic effect of sucrose and tung oil. After 384 h of immersion, the 30% sucrose and tung oil group presented a reduction in water absorption by 76.7% compared to the control group, and the anti-swelling efficiency was 57.85%, which was 66.81% higher than that of the tung oil treatment alone. Additionally, the leaching rate of the 30% sucrose and tung oil group decreased by 81.27% compared to the sample modified with the 30% sucrose solution alone. Simultaneously, the 30% sucrose and tung oil group showed better thermal stability. Therefore, this study demonstrates that the synergistic treatment of modified rubber wood by sucrose and tung oil is an eco-friendly, economical, and highly efficient approach with the potential to expand the range of applications of rubber wood products.

The seed oil of tung tree is rich in a-eleostearic acid (ESA), which endows tung oil with the characteristic of an excellently dry oil. The stearoyl-acyl carrier protein δ9 desaturase (SAD) is a rate-limiting enzyme that converts the stearic acid to the oleic acid, the substrate for the production of the α-ESA. However, the function of the two predicted VfSAD1 and VfSAD2 genes in the tung tree has not been determined. In this study, quantitative real-time PCR (qRT-PCR) analysis showed that VfSAD1 and VfSAD2 were expressed in multiple organs of tung tree but were highly expressed in the seed during the oil rapid accumulation period. Heterologous expression of VfSAD1 and VfSAD2 could promote the production of oleic acid and its derivatives in Arabidopsis thaliana and yeast BY4741, indicating that VfSAD1 and VfSAD2 possess the stearoyl-ACP desaturases function. Furthermore, both VfSAD1 and VfSAD2 could significantly improve seed oil accumulation in Arabidopsis. VfSAD1 could also significantly promote the oil accumulation in the yeast BY4741 strain. In addition, overexpression of VfSAD1 and VfSAD2 enhanced the tolerance of yeast and Arabidopsis seedlings to low temperature stress. This study indicates that the two VfSAD genes play a vital role in the process of oil accumulation and fatty acid biosynthesis in the tung tree seed, and both of them could be used for molecular breeding in tung tree and other oil crops.

Tung wilt disease, caused by Fusarium oxysporum f. sp. fordiis (Fof‐1), poses a serious threat to tung oil tree (Vernicia fordii) production. Fortunately, another native Vernicia species in China, V. montana (woody tung oil tree) exhibits high resistance ability to the pathogen. The resistant and susceptible tung trees provide material for the investigation on the mechanism underlying the resistance to Fusarium wilt disease. Root xylem extracts of resistant V. montana significantly inhibited Fof‐1 growth compared with that of susceptible V. fordii. Metabolomic analysis of V. montana root xylem revealed that 13 types of flavonoids increased after Fof‐1 infection. Of the 13 flavonoids, antimicrobial assays showed that catechin, (−)‐epicatechin and (−)‐epigallocatechin exhibited an obvious inhibitory effect on Fof‐1 growth. Transcriptomic analysis revealed that several genes with up‐regulated expression patterns were also enriched in the flavonoid biosynthesis pathway after Fof‐1 infection in V. montana. Among them, the anthocyanidin reductase (ANR) gene is directly involved in the biosynthesis of antimicrobial (−)‐epicatechin and (−)‐epigallocatechin. Moreover, transgenic V. montana lines overexpressing the VmANR gene elevated eight types of flavonoid concentrations, and silencing VmANR resulted in a substantial reduction in the levels of catechin and myricitrin. The enzyme activity assay in vitro further verified that VmANR catalysed the formation of (−)‐epigallocatechin from the substrate cyanidin. This study identifies VmANR as a critical gene to promote biosynthesis of antimicrobial flavonoids in shaping resistance to Fof‐1 infection, and offers an effective strategy for breeding Fusarium‐resistant tung oil trees. Root xylem extract of resistant V. montana inhibited Fof‐1 growth. After Fof‐1 infection, we screened the increased 13 types of flavonoids and the up‐regulated eight genes in the flavonoid biosynthesis in V. montana. VmANR overexpression enhanced the flavonoid content, with catechin, (−)‐epicatechin and (−)‐epigallocatechin inhibiting Fof‐1 growth.

Background Oil from seeds of the tung tree ( Vernicia fordii) has unique drying properties that are industrially important. We found that the extended oil accumulation period was related to the high seed oil content at maturity among tung tree population. In order to understand the molecular mechanism underlying the high oil content in tung tree seed, Tree H and L were adopted for the further investigation, with seed oil content of about 70 and 45%, respectively. We compared the transcriptomic changes of seed at various times during oil accumulation between the two trees. Results Transcriptomes analysis revealed that many genes involved in glycolysis, fatty acid synthesis, and tri-acyl glyceride assembly still kept high expression in the late period of seed oil accumulation for Tree H only. Many genes in fatty acid degradation pathway were largely up regulated in the late period of seed oil accumulation for Tree L only. Four transcription factors related to fatty acid biosynthesis had different expression pattern in the seed oil accumulation period for the two trees. WRI1 was down regulated and kept the low expression in the late period of seed oil accumulation for the two trees. PII , LEC1 and LEC1-LIKE extended the high expression in the late period of seed oil accumulation in Tree H only. Conclusions The continued accumulation of oil in the late period of seed oil accumulation for Tree H was associated with relatively high expression of the relevant genes in glycolysis, fatty acid synthesis and tri-acyl glyceride assembly. PII , LEC1, and LEC1-LIKE rather than WRI1 should play an important role in the oil continual accumulation in the late period of seed oil accumulation in Tree H. This study provides novel insight into the variation in seed oil content and informs plant breeding strategies to maximize oil yield.

Tung oil contains approximately 78% α -eleostearic acid (9 c , 11 t , 13 t -octadecatrienoic acid), 9% linoleic acid, and 7% oleic acid. This oil is easily oxidized because of the three conjugated double bonds in α -eleostearic acid; however, it is stable within the tung seed. Previously, we isolated and identified a catechol-type lignan and neolignans from tung seeds, which exhibited potent antioxidant activity. Catechol compounds were specifically present in the seed coat of tung trees. In this study, we quantified the catechol-type lignans in the seed coat of Euphorbiaceae oil-producing plants and found that the plant seeds containing easily oxidized fatty acids contained higher amounts of catechol-type lignans in their seed coat. The antioxidant activity assay of phenolic compounds indicated that catechol-type compounds have higher antioxidant activity than monophenol-type compounds, and that the two hydroxy groups in the ortho -position of the benzene ring are important for enhancing antioxidant activity. Analysis of the antioxidant mechanism by 13 C nuclear magnetic resonance ( 13 C NMR) spectroscopy showed that isoamericanol A captured the 2, 2-diphenyl-1-picrylhydrazyl (DPPH) radical and preferentially changed it to the quinone structure. The oil oxidation inhibition test revealed that α -tocopherol inefficiently inhibited the oxidation of tung oil, and that catechol compounds with a higher antioxidative activity than α -tocopherol would be required to prevent the oxidation of tung oil. These results show that tung seeds synthesize catechol-type lignans in the seed coat to prevent the oxidation of tung oil in the endosperm.

Tung tree (Vernicia fordii) provides the sole source of tung oil widely used in industry. Lack of fatty acid composition and molecular markers hinders biochemical, genetic and breeding research. The objectives of this study were to determine fatty acid profiles and develop unigene-derived simple sequence repeat (SSR) markers in tung tree. Fatty acid profiles of 41 accessions showed that the ratio of α-eleostearic acid was increasing continuously with a parallel trend to the amount of tung oil accumulation while the ratios of other fatty acids were decreasing in different stages of the seeds and that α-eleostearic acid (18∶3) consisted of 77% of the total fatty acids in tung oil. Transcriptome sequencing identified 81,805 unigenes from tung cDNA library constructed using seed mRNA and discovered 6,366 SSRs in 5,404 unigenes. The di- and tri-nucleotide microsatellites accounted for 92% of the SSRs with AG/CT and AAG/CTT being the most abundant SSR motifs. Fifteen polymorphic genic-SSR markers were developed from 98 unigene loci tested in 41 cultivated tung accessions by agarose gel and capillary electrophoresis. Genbank database search identified 10 of them putatively coding for functional proteins. Quantitative PCR demonstrated that all 15 polymorphic SSR-associated unigenes were expressed in tung seeds and some of them were highly correlated with oil composition in the seeds. Dendrogram revealed that most of the 41 accessions were clustered according to the geographic region. These new polymorphic genic-SSR markers will facilitate future studies on genetic diversity, molecular fingerprinting, comparative genomics and genetic mapping in tung tree. The lipid profiles in the seeds of 41 tung accessions will be valuable for biochemical and breeding studies.

The tung oil tree, Vernicia fordii (formerly Aleurites fordii ), is used to produce biodiesel, and inter-row spacing during the cultivation of these trees allows other species to be grown alongside them, such as oilseeds. However, the sustainability of these intercropping systems in regard to greenhouse gas emissions and biodiesel oil production capacity is unknown. Hence, this study evaluated four intercropping systems during the initial establishment phase of tung trees over three growing seasons, namely: crambe ( Crambe abyssinica )/sunflower ( Helianthus annuus )/crambe with mineral fertilizer, crambe/sunflower/crambe with organic fertilizer; oat + vetch ( Avena strigosa  +  Vicia sativa )/peanut ( Arachis hypogaea L.)/oat + vetch without fertilizer, and fallow/fallow/fallow with the inter-rows left uncultivated. We measured methane (CH 4 ) and nitrous oxide (N 2 O) emissions from the soil and estimated oil production, carbon (C) saving, and global warming potential (GWP) in each system. Peanut grain production surpasses that of sunflower and crambe, resulting in a higher oil yield when compared to non-legume oilseeds. Cumulative N 2 O emissions were higher ( p  < 0.05) with intercropping compared to the fallow, varying from 0.18 to 1.42% with mineral fertilizer and 0.15–0.90% for organic fertilizer. However, there was no difference ( p  < 0.05) between the two N sources over the three growing seasons. Meanwhile, CH 4 oxidation in the soil was lower when organic fertilization was used. The intercropping system with cover crops in the winter and peanuts in the summer presented the greater C saving (4.81 Mg CO 2 eq ha −1 ) resulting in the more negative GWP (− 3.87 Mg CO 2 eq ha −1 ). This is the first study to evaluate the energy potential and C savings of different intercropping systems with tung oil trees. Our findings indicated that the sustainability of the production system can be increased when oilseed crops are intercropped with tung trees.