Extraction of antimicrobial peptides from pea protein hydrolysates by sulfonic acid functionalized biochar.

The extraction methods for antimicrobial peptides (AMPs) from plants are varied, but the absence of a standardized and rapid technique remains a challenge. In this study, a functionalized biochar was developed and characterized for the extraction of AMPs from pea protein hydrolysates. The results indicated that the biochar mainly enriched AMPs through electrostatic interaction, hydrogen bonding and pore filling. Then three novel cationic antimicrobial peptides were identified, among which the RDLFK (Arg-Asp-Leu-Phe-Lys) had the greatest inhibitory effect against Staphylococcus aureus and Bacillus subtilis, showcasing IC50 value of 2.372 and 1.000 mg/mL, respectively. Additionally, it was found that RDLFK could damage bacterial cell membranes and penetrate the cells to inhibit DNA synthesis. These results provided that the biochar-based extraction method presents an efficient and promising avenue for isolating AMPs, addressing a critical gap in the current methodologies for their extraction from plant sources.

Explosion-puffing pretreatment effect on the microstructure of Camellia oleifera Abel. seed and the quality of its oil.

To improve the extraction process and quality of Camellia oleifera Abel. oil (COO). This study examined the influence of explosion-puffing (EP) pretreatment on the physicochemical properties, characteristic compounds and sensory quality of the COO. The results revealed that the seeds after EP pretreatment had cavities surface, which facilitated the extraction of the COO and the dissolution of bioactive compounds. Compared to the untreated group, the oil yield of the 6-7%/20 min was increased from 71.41 to 88.94%, as well as higher levels of squalene, phytosterol, α-tocopherol, and phenolic acids, leading to an increase in the antioxidant abilities. Moreover, the fatty acid composition in the COO was not significantly affected (P > 0.05). W1C, W5S, W3C, W5C, and W1W were the main sensors to distinguish the flavor profile of the COO. In summary, EP pretreatment may be a promising method for enhancing oil yield and quality of the COO.

Genome-Wide Analyses of MADS-Box Genes Reveal Their Involvement in Seed Development and Oil Accumulation of Tea-Oil Tree (Camellia oleifera).

The seeds of Camellia oleifera produce high amount of oil, which can be broadly used in the fields of food, industry, and medicine. However, the molecular regulation mechanisms of seed development and oil accumulation in C. oleifera are unclear. In this study, evolutionary and expression analyses of the MADS-box gene family were performed across the C. oleifera genome for the first time. A total of 86 MADS-box genes (ColMADS) were identified, including 60 M-type and 26 MIKC members. More gene duplication events occurred in M-type subfamily (6) than that in MIKC subfamily (2), and SEP-like genes were lost from the MIKCC clade. Furthermore, 8, 15, and 17 differentially expressed ColMADS genes (DEGs) were detected between three developmental stages of seed (S1/S2, S2/S3, and S1/S3), respectively. Among these DEGs, the STK-like ColMADS12 and TT16-like ColMADS17 were highly expressed during the seed formation (S1 and S2), agreeing with their predicted functions to positively regulate the seed organogenesis and oil accumulation. While ColMADS57 and ColMADS07 showed increasing expression level with the seed maturation (S2 and S3), conforming to their potential roles in promoting the seed ripening. In all, these results revealed a critical role of MADS-box genes in the C. oleifera seed development and oil accumulation, which will contribute to the future molecular breeding of C. oleifera.

Analysis and evaluation of Camellia oleifera Abel. Germplasm fruit traits from the high-altitude areas of East Guizhou Province, China.

Camellia oleifera, a significant woody edible oil species, was examined using 48 germplasm resources from high-altitude regions in East Guizhou Province, China, to analyze fruit quality. The analysis aimed to identify high-performance germplasm, providing theoretical and research foundations for selecting and cross-breeding superior C. oleifera varieties in these regions. Fifteen primary traits of mature fruits were measured and analyzed, including four phenotypic traits (single fruit weight, transverse diameter, longitudinal diameter, peel thickness) and eleven quality traits (fresh seed yield rate, dry seed yield rate, dry kernel yield rate, seed kernel oil content, palmitic acid, palmitoleic acid, stearic acid, oleic acid, linoleic acid, α-linolenic acid, cis-11-eicosenoic acid). A comprehensive evaluation employing cluster and principal component analyses (PCA) was conducted. The cluster analysis categorized the germplasms into five groups at a squared Euclidean distance of 14, with the first category comprising 17 germplasms, the second 28, and the third, fourth, and fifth each containing one. PCA reduced the 15 traits to five principal components (PCs), with PC1 having the highest eigenvalue of 3.57 and a contribution rate of 23.8%, mainly representing phenotypic traits. PC2, contributing 20.44%, represented linoleic acid, while PC3, PC4, and PC5, with contribution rates of 12.99%, 9.13%, and 7.45% respectively, predominantly represented seed kernel oil content, fresh seed yield, and palmitoleic acid. Employing a weighted sum method, a comprehensive evaluation function was developed to calculate total scores for each superior individual, forming the basis for rankings and selections. Notable variability was detected in single fruit weight, peel thickness, and fresh and dry seed yields, while oleic acid exhibited the lowest coefficient of variation. Dry seed yield showed a robust positive correlation with seed kernel oil content and the concentrations of palmitic and linoleic acids, whereas seed kernel oil content was inversely correlated with cis-11-eicosenoic acid levels. Five PCs with eigenvalues > 1 were identified, highlighting the top ten superior individuals: QD (Qian Dong: the code of eastern Guizhou Province)-33 > QD-34 > QD-48 > QD-38 > QD-27 > QD-15 > QD-35 > QD-5 > QD-14 > QD-36. Thus, the 48 C. oleifera germplasms from East Guizhou's high-altitude areas demonstrate significant potential for enhancing traits such as single fruit weight, peel thickness, and fresh and dry seed yields. Specifically, QD-33, QD-34, and QD-48 exhibited superior comprehensive performance, designating them as prime candidates for variety selection and breeding.

Catalytic depolymerization of Camellia oleifera shell lignin to phenolic monomers: Insights into the effects of solvent, catalyst and atmosphere.

Camellia oleifera shell (COS) is a renewable biomass resource abundant in lignin with significant potential for producing phenolic monomers. However, the dearth of research has led to considerable resource wastage and environmental pollution. Herein, reductive catalytic fractionation (RCF) of COS was performed using noble metal catalysts in different solvents. An 11.1 wt% yield of phenolic monomers was achieved with 91% selectivity toward propylene-substituted monomers in H2O/EtOH (3:7, v/v) cosolvent under N2 atmosphere. Notably, the highest phenolic monomer yield of 17.0 wt% was obtained with impressive selectivity (86.9%) toward propanol-substituted monomers in the presence of H2. The GPC analysis and 2D HSQC NMR spectra indicated the effective depolymerization of lignin oligomers with catalysts. Phenolic monomers with ethyl, propyl, or propanol side chain could be produced from lignin-derived oligomers through hydrogenolysis, hydrogenation, and decarboxylation reactions. Overall, this study has paved the way for the valorization of COS lignin through the RCF strategy.

Transcriptome analysis unravels key pathways and hub genes related to immature fruit abscission in Camellia oleifera.

Immature fruit abscission of Camellia oleifera (C. oleifera) is a common problem limiting yield increases. However, the regulatory mechanisms underlying immature fruit abscission in C. oleifera are unclear. In this study, we systematically investigated changes in the morphological, physiological, and gene expression of fruit abscission zones (FAZs) of soon-to-abscise fruits (M2). We found that fruit abscission before ripening mainly occurs during the August abscission stage of 'Huashuo'. At the beginning of this stage, the FAZs of M2 have a marked dent, and the separation layer structures are preliminarily formed. Phytohormone analysis showed that the contents of indole-3-acetic acid (IAA) and jasmonic acid (JA) in the FAZs of M2 were significantly decreased compared with the non-abscised fruits, while the content of trans-zeatin (TZR) was increased. Transcriptome analysis identified differentially expressed genes (DEGs) mainly involved in phytohormone metabolism, including ethylene, auxin, JA, and the cis-zeatin signal transduction pathway. There were also many DEGs involved in cell wall catabolism. Weighted gene co-expression network analysis (WGCNA) further suggested that the transcription factors NAC100 and ERF114 participate in the immature fruit abscission of C. oleifera. This study provides insights into the fruit abscission mechanism of C. oleifera.

Cataloging the Genetic Response: Unveiling Drought-Responsive Gene Expression in Oil Tea Camellia (Camellia oleifera Abel.) through Transcriptomics.

Drought stress is a critical environmental factor that significantly impacts plant growth and productivity. However, the transcriptome analysis of differentially expressed genes in response to drought stress in Camellia oleifera Abel. is still unclear. This study analyzed the transcriptome sequencing data of C. oleifera under drought treatments. A total of 20,674 differentially expressed genes (DEGs) were identified under drought stress, with the number of DEGs increasing with the duration of drought. Specifically, 11,793 and 18,046 DEGs were detected after 8 and 15 days of drought treatment, respectively, including numerous upregulated and downregulated genes. Gene Ontology (GO) enrichment analysis showed that the DEGs were primarily involved in various biological processes. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis revealed that carbon metabolism, glyoxylate and dicarboxylate metabolism, proteasome, glycine, serine, and threonine metabolism were the main affected pathways. Among the DEGs, 376 protein kinases, 42 proteases, 168 transcription factor (TF) genes, and 152 other potential functional genes were identified, which may play significant roles in the drought response of C. oleifera. The expression of relevant functional genes was further validated using quantitative real-time PCR (qRT-PCR). These findings contribute to the comprehension of drought tolerance mechanisms in C. oleifera and bolster the identification of drought-resistant genes for molecular breeding purposes.

ABA and MeJA Induced Catechin and Epicatechin Biosynthesis and Accumulation in Camellia oleifera Fruit Shells.

Camellia oleifera Abel, one of the most valuable woody oil plants, has been widely cultivated for extracting edible oil. The shell of C. oleifera is a by-product generated in the processing of edible oil extraction. However, there is still limited research on the maturity and high-value resource utilization of shell by-products. We found that the C. oleifera 'Huashuo' (HS) fruit shells contained a high content of catechins. Abscisic acid (ABA) and methyl jasmonate (MeJA) enhanced the accumulation of catechins in C. oleifera fruit shells, providing a basis for production and application of the catechins in fruit shells of C. oleifera. We further found that 500 µM ABA and 900 µM MeJA significantly promoted the accumulation of catechin (C) and epicatechin (EC) in fruit shells. Following treatment with 900 µM MeJA, the expressions of CoPAL1, CoC4H1, CoC4H2, CoC4H3, Co4CL1, Co4CL2, CoF3'H1, CoLAR1, CoLAR2, CoLAR3, CoANR2, and CoANRL2 were significantly upregulated, while after 500 µM ABA treatment the expressions of CoPAL3, CoCHS1, CoCHS4, CoF3'H1, CoDFR, CoLAR1, CoLAR2, CoLAR3, CoANS1, CoANR1, and CoANR2 increased dramatically. These results indicate that appropriate concentrations of ABA and MeJA activate C and EC biosynthesis and promote their accumulation in fruit shells. Our results provide new ideas and guidance for promoting the resource utilization of C. oleifera fruit shells.

CTDUNet: A Multimodal CNN-Transformer Dual U-Shaped Network with Coordinate Space Attention for Camellia oleifera Pests and Diseases Segmentation in Complex Environments.

Camellia oleifera is a crop of high economic value, yet it is particularly susceptible to various diseases and pests that significantly reduce its yield and quality. Consequently, the precise segmentation and classification of diseased Camellia leaves are vital for managing pests and diseases effectively. Deep learning exhibits significant advantages in the segmentation of plant diseases and pests, particularly in complex image processing and automated feature extraction. However, when employing single-modal models to segment Camellia oleifera diseases, three critical challenges arise: (A) lesions may closely resemble the colors of the complex background; (B) small sections of diseased leaves overlap; (C) the presence of multiple diseases on a single leaf. These factors considerably hinder segmentation accuracy. A novel multimodal model, CNN-Transformer Dual U-shaped Network (CTDUNet), based on a CNN-Transformer architecture, has been proposed to integrate image and text information. This model first utilizes text data to address the shortcomings of single-modal image features, enhancing its ability to distinguish lesions from environmental characteristics, even under conditions where they closely resemble one another. Additionally, we introduce Coordinate Space Attention (CSA), which focuses on the positional relationships between targets, thereby improving the segmentation of overlapping leaf edges. Furthermore, cross-attention (CA) is employed to align image and text features effectively, preserving local information and enhancing the perception and differentiation of various diseases. The CTDUNet model was evaluated on a self-made multimodal dataset compared against several models, including DeeplabV3+, UNet, PSPNet, Segformer, HrNet, and Language meets Vision Transformer (LViT). The experimental results demonstrate that CTDUNet achieved an mean Intersection over Union (mIoU) of 86.14%, surpassing both multimodal models and the best single-modal model by 3.91% and 5.84%, respectively. Additionally, CTDUNet exhibits high balance in the multi-class segmentation of Camellia oleifera diseases and pests. These results indicate the successful application of fused image and text multimodal information in the segmentation of Camellia disease, achieving outstanding performance.

High-Density Genetic Map Construction and Quantitative Trait Locus Analysis of Fruit- and Oil-Related Traits in Camellia oleifera Based on Double Digest Restriction Site-Associated DNA Sequencing.

Camellia oleifera, an important tree species and source of edible oil in China, has received significant attention owing to the oil's high unsaturated fatty acid content, which has benefits for human health. However, the mechanisms underlying C. oleifera yield and oil quality are largely unknown. In this study, 180 F1 progenies were obtained from two parents with obvious differences in fruit- and oil-related traits. We constructed a high-density genetic map using a double digest restriction site-associated DNA sequencing (ddRAD-Seq) strategy in C. oleifera. This map spanned 3327 cM and anchored 2780 markers in 15 linkage groups (LGs), with an average marker interval of 1.20 cM. A total of 221 quantitative trait loci (QTLs) associated with fruit- and oil-related traits were identified across three years' worth of phenotypic data. Nine QTLs were detected simultaneously in at least two different years, located on LG02, LG04, LG05, LG06, and LG11, and explained 8.5-16.6% of the phenotypic variation in the corresponding traits, respectively. Seventeen major QTLs were obtained that explained 13.0-16.6% of the phenotypic variance. Eleven and five flanking SNPs of major QTLs for fruit- and oil-related traits were detected which could be used for marker-assisted selection in C. oleifera breeding programs. Furthermore, 202 potential candidate genes in QTL regions were identified based on the collinearity of the genetic map and the C. oleifera "CON" genome. A potential regulatory network controlling fruit development and oil biosynthesis was constructed to dissect the complex mechanism of oil accumulation. The dissection of these QTLs will facilitate the gene cloning underlying lipid synthesis and increase our understanding in order to enhance C. oleifera oil yield and quality.

Vernicia fordii leaf extract inhibited anthracnose growth by downregulating reactive oxygen species (ROS) levels in vitro and in vivo.

Background: Colletotrichum fructicola is a predominant anthracnose species in Camellia oleifera, causing various adverse effects. Traditional intercropping Vernicia fordii with C. oleifera may enhance anthracnose resistance, but the mechanism remains elusive. Methods: We utilized UPLC-MS/MS and acid-base detection to identify the major antimicrobial alkaloid components in the V. fordii leaf extract. Subsequently, by adding different concentrations of V. fordii leaf extract for cultivating C. fructicola, with untreated C. fructicola as a control, we investigated the impact of the V. fordii leaf extract, cell wall integrity, cell membrane permeability, MDA, and ROS content changes. Additionally, analysis of key pathogenic genes of C. fructicola confirmed that the V. fordii leaf extract inhibits the growth of the fungus through gene regulation. Results: This study discovered the alkaloid composition of V. fordii leaf extract by UPLC-MS/MS and acid-base detection, such as trigonelline, stachydrine, betaine, and O-Phosphocholine. V. fordii leaf extract successfully penetrated C. fructicola mycelia, damaged cellular integrity, and increased ROS and MDA levels by 1.75 and 2.05 times respectively, thereby inhibiting C. fructicola proliferation. By analyzing the key pathogenic genes of C. fructicola, it was demonstrated that the antifungal function of V. fordii leaf extract depends mainly on the regulation of RAB7 and HAC1 gene expression. Therefore, this study elucidates the mechanism of V. fordii -C. oleifera intercropping in strengthening anthracnose resistance in C. oleifera, contributing to efficient C. oleifera cultivation.

Comparative Transcriptomic and Lipidomic Analysis of Fatty Acid Accumulation in Three Camellia oleifera Varieties During Seed Maturing.

Camellia oleifera, a major woody oil crop in China, produces tea oil rich in unsaturated fatty acids, earning it names like liquid gold and eastern olive oil. This study provides an integrated investigation of the transcriptome and lipidome within seeds at the maturing process across three C. oleifera varieties, revealing a significant relationship between fatty acid production and genes involved in lipid synthesis. Through transcriptomic analysis, 26,344 genes with varied expression were found. Functional enrichment analysis highlighted that pathways related to starch and sucrose metabolism, plant hormone signal transduction, and lipid accumulation were highly enriched among the differentially expressed genes. Coordinated high expression of key genes (ACCase, KAS I, KAS II, KAS III, KAR, HAD, EAR, SAD, LPAAT, LACS, DGAT, PDAT) during the late maturation stage contributes largely to high oil content. Additionally, expression variations of SAD and FADs among different varieties were explored. The analysis suggests that high expression of genes such as FAD3, FAD7, and FAD8 notably increased linolenic acid content. This research provides new insights into the molecular mechanisms of oil biosynthesis in C. oleifera, offering valuable references for improving yield and quality.

Comparative physiological and transcriptomic analyses provide induction resistance mechanisms of Bacillus tequilensis against Colletotrichum fructicola in Camellia oleifera.

Bacillus tequilensis DZY 6715 was isolated from healthy leaves in Camellia oleifera, and the strain DZY 6715 significantly inhibited anthracnose disease resulting from Colletotrichum fructicola in C. oleifera, besides, its associated mechanism of disease resistance was explored. B. tequilensis DZY 6715 treatment controlled mycelial growth of C. fructicola in C. oleifera, and significantly decreased C. oleifera anthracnose incidence and disease index compared with the control group. B. tequilensis DZY 6715 has strong biofilm forming ability, and also secretes extracellular ß-1, 3-glucanase and chitinase, which could cause cell membranes damage and increased cellular compound leakage. C.oleifera treated with DZY 6715 also effectively enhanced enzyme activities and stimulated the synthesis the substances related to phenylpropane metabolism and reactive oxygen metabolism. Moreover, transcript profiling analysis revealed more differentially expressed genes related to phenylpropanoid pathway metabolism and antioxidant system inducing by DZY 6715 compared with the control in C. oleifera. Thus, it can be concluded that B. tequilensis DZY 6715 is a suitable bio-control agent to control anthracnose disease in C. oleifera.

Effects of Camellia oleifera seed shell polyphenols and 1,3,6-tri-O-galloylglucose on androgenic alopecia via inhibiting 5a-reductase and regulating Wnt/ß-catenin pathway.

Androgenetic alopecia (AGA) is the leading cause of hair loss in adults. Its pathogenesis remains unclear, but studies have shown that the androgen-mediated 5α-reductase-AR receptor pathway and the Wnt/ß-catenin signaling pathway play significant roles. Camellia oleifera is an oil plant, and its fruits have been documented in folklore as having a hair cleansing effect and preventing hair loss. In this study, we used UPLC-Q-TOF-MS/MS to identify the structure of the substances contained in the polyphenols of Camellia oleifera seed shell. These polyphenols are mainly used for shampooing and anti-hair loss purposes. Next, we used molecular docking technology to dock 41 polyphenols and steroidal 5 alpha reductase 2 (SRD5A2). We found that the docking scores and docking sites of 1,3,6-tri-O-galloylglucose (TGG) and finasteride were similar. We constructed a mouse model of DHT-induced AGA to evaluate the effects of Camellia oleifera seed shell polyphenols (CSSP) and TGG in vivo. Treatment with CSSP and TGG alleviated alopecia symptoms and reduced DHT levels. Additionally, CSSP and TGG were able to reduce androgen levels by inhibiting the SRD5A2-AR receptor signaling pathway. Furthermore, by regulating the secretion of growth factors and activating the Wnt/ß-catenin signaling pathway, CSSP and TGG were able to extend the duration of hair growth. In conclusion, our study showed that CSSP and TGG can improve AGA in C57BL/6 J mice and reduce the effect of androgen on hair follicle through the two signaling pathways mentioned above. This provides new insights into the material basis and mechanism of the treatment of AGA by CSSP.

Robust holocellulose barrier films from agricultural byproduct of Camellia Oleifera shells through dilute acid and ultrasonic treatments.

Camellia oleifera shells (COS) are commonly discarded as an agricultural by-product. Effective utilization of COS can not only reduce environmental pollution but also enhance the value of the tea-oil industry. The unique composition of COS, with high hemicellulose and low cellulose content, makes it suitable for the production of film materials. In this study, COS holocellulose (COSH) was isolated and treated with four different types of dilute acids (15 % acetic acid, gallic acid, citric acid, and 0.5 % sulfuric acid, 1-24 h, 75°-105 °C) to produce barrier films. Among these, citric acid treatment resulted in the strongest and toughest film. By incorporating a brief ultrasonic pretreatment (15 min, 300 w) prior to the citric acid reaction, translucent films were achieved with impressive mechanical properties, showing tensile strength, Young's modulus and elongation at break up to 75.72 MPa, 3306.11 MPa and 8.01 %, respectively. Through a comprehensive analysis of the structure-property relationships, it was discovered that the combined effects of ultrasonic and citric acid treatments disrupted the integrated holocelluose fiber structure and facilitated the formation of a robust hydrogen bond network during the film preparation process. The resulting films exhibited enhanced water vapor barrier properties, antioxidant capacity, and complete decomposition in soil, suggesting the potential application as wraps for fresh fruits.

UPLC-MS/MS reveals the differences in lipids composition of Camellia oleifera from northern margin distribution area.

The lipids accumulation characteristics in 23Camellia oleifera lines from northern margin distribution area were investigated through quantitative lipidomics. Combined lipids content-function analysis indicated that NQ1, HT1, HT2, ZA2, ZB1, ZB2, and SN2 lines had potential to develop functional foods due to abundant glycerolipids (GLs), glycerophospholipids (GPs), fatty acids (FAs), and prenol lipids (PRs). 673 lipids components were detected, and 293 differential components were identified in NQ1, ZA2, HB1, and HT1. 4 kinds free fatty acids (FFAs) were higher in NQ1, 5 triglycerides (TGs) were higher in HT1, and 2 phosphatidyl serines (PSs) and 1 phosphatidyl glycerol (PG) were higher in ZA2. GLs, GPs, and FFAs had strong relation at intra- and inter-category level. Glycerolipid metabolism, glycerophospholipid metabolism, and fatty acid biosynthesis were the significantly differential lipids pathways. Our study elucidated lipids differences of 23 C. oleifera lines, and offered valuable references for lipids biosynthesis, directional breeding, and lipids utilization.

Integrated analysis of miRNAs, transcriptome and phytohormones in the flowering time regulatory network of tea oil camellia.

Camellia oleifera is a crucial cash crop in the southern region of China. Timely flowering is a crucial characteristic for maximizing crop productivity. Nevertheless, the cold temperature and wet weather throughout the fall and winter seasons in South China impact the timing of flowering and the yield produced by C. oleifera. This study examined the miRNAs, transcriptomes, and phytohormones that are part of the flowering time regulatory networks in distinct varieties of C. oleifera (Sep, Oct, and Nov). This study provides evidence that phytohormones significantly impact the timing of flowering in C. oleifera leaves. There is a positive correlation between the accumulation variations of zeatin (cZ), brassinolide (BL), salicylic acid (SA), 1-amino cyclopropane carboxylic acid (ACC), and jasmonic acid (JA) and flowering time. This means that blooming occurs earlier when the quantity of these substances in leaves increases. Abscisic acid (ABA), trans-zeatin-riboside (tZR), dihydrozeatin (dh-Z), and IP (N6-Isopentenyladenine) exhibit contrasting effects. Furthermore, both miR156 and miR172 play a crucial function in regulating flowering time in C. oleifera leaves by modulating the expression of SOC1, primarily through the miR156-SPL and miR172-AP2 pathways. These findings establish a strong basis for future research endeavors focused on examining the molecular network associated with the flowering period of C. oleifera and controlling flowering time management through external treatments. Supplementary Information: The online version contains supplementary material available at 10.1007/s12298-024-01473-2.

Effects of nitrogen deposition on the rhizosphere nitrogen-fixing bacterial community structure and assembly mechanisms in Camellia oleifera plantations.

Increased nitrogen deposition is a key feature of global climate change, however, its effects on the structure and assembling mechanisms of the nitrogen-fixing bacteria present at the root surface remain to be elucidated. In this pursuit, we used NH4NO3 to simulate nitrogen deposition in a 10-year-old Camellia oleifera plantation, and set up four deposition treatments, including control N0 (0 kg N hm-2 a-1), low nitrogen N20 (20 kg N hm-2 a-1), medium nitrogen N40 (40 kg N hm-2 a-1) and high nitrogen N160 (160 kg N hm-2 a-1). The results showed that nitrogen deposition affected the soil nitrogen content and the structure of the nitrogen-fixing bacterial community. Low nitrogen deposition was conducive for nitrogen fixation in mature C. oleifera plantation. With increasing nitrogen deposition, the dominant soil nitrogen-fixing bacterial community shifted from Desulfobulbaceae to Bradyrhizobium. When nitrogen deposition was below 160 kg N hm-2 a-1, the soil organic matter content, total nitrogen content, nitrate nitrogen content, ammonium nitrogen content, urease activity, soil pH and nitrate reductase activity influenced the composition of the nitrogen-fixing bacterial community, but the stochastic process remained the dominant factor. The results indicate that the strains of Bradyrhizobium japonicum and Bradyrhizobium sp. ORS 285 can be used as indicator species for excessive nitrogen deposition.

Genome-wide identification and molecular evolution of Dof gene family in Camellia oleifera.

DNA binding with one finger(Dof) gene family is a class of transcription factors which play an important role on plant growth and development. Genome-wide identification results indicated that there were 45 Dof genes(ColDof) in C.oleifera genome. All 45 ColDof proteins were non-transmembrane and non-secretory proteins. Phosphorylation site analysis showed that biological function of ColDof proteins were mainly realized by phosphorylation at serine (Ser) site. The secondary structure of 44 ColDof proteins was dominated by random coil, and only one ColDof protein was dominated by α-helix. ColDof genes' promoter region contained a variety of cis-acting elements, including light responsive regulators, gibberellin responsive regulators, abscisic acid responsive regulators, auxin responsive regulators and drought induction responsive regulators. The SSR sites analysis showed that the proportion of single nucleotide repeats and the frequency of A/T in ColDof genes were the largest. Non-coding RNA analysis showed that 45 ColDof genes contained 232 miRNAs. Transcription factor binding sites of ColDof genes showed that ColDof genes had 5793 ERF binding sites, 4381 Dof binding sites, 2206 MYB binding sites, 3702 BCR-BPC binding sites. ColDof9, ColDof39 and ColDof44 were expected to have the most TFBSs. The collinearity analysis showed that there were 40 colinear locis between ColDof proteins and AtDof proteins. Phylogenetic analysis showed that ColDof gene family was most closely related to that of Camellia sinensis var. sinensis cv.Biyun and Camellia lanceoleosa. Protein-protein interaction analysis showed that ColDof34, ColDof20, ColDof28, ColDof35, ColDof42 and ColDof26 had the most protein interactions. The transcriptome analysis of C. oleifera seeds showed that 21 ColDof genes were involved in the growth and development process of C. oleifera seeds, and were expressed in 221 C. oleifera varieties. The results of qRT-PCR experiments treated with different concentrations NaCl and PEG6000 solutions indicated that ColDof1, ColDof2, ColDof14 and ColDof36 not only had significant molecular mechanisms for salt stress tolerance, but also significant molecular functions for drought stress tolerance in C. oleifera. The results of this study provide a reference for further understanding of the function of ColDof genes in C.oleifera.

The complex hexaploid oil-Camellia genome traces back its phylogenomic history and multi-omics analysis of Camellia oil biosynthesis.

Oil-Camellia (Camellia oleifera), belonging to the Theaceae family Camellia, is an important woody edible oil tree species. The Camellia oil in its mature seed kernels, mainly consists of more than 90% unsaturated fatty acids, tea polyphenols, flavonoids, squalene and other active substances, which is one of the best quality edible vegetable oils in the world. However, genetic research and molecular breeding on oil-Camellia are challenging due to its complex genetic background. Here, we successfully report a chromosome-scale genome assembly for a hexaploid oil-Camellia cultivar Changlin40. This assembly contains 8.80 Gb genomic sequences with scaffold N50 of 180.0 Mb and 45 pseudochromosomes comprising 15 homologous groups with three members each, which contain 135 868 genes with an average length of 3936 bp. Referring to the diploid genome, intragenomic and intergenomic comparisons of synteny indicate homologous chromosomal similarity and changes. Moreover, comparative and evolutionary analyses reveal three rounds of whole-genome duplication (WGD) events, as well as the possible diversification of hexaploid Changlin40 with diploid occurred approximately 9.06 million years ago (MYA). Furthermore, through the combination of genomics, transcriptomics and metabolomics approaches, a complex regulatory network was constructed and allows to identify potential key structural genes (SAD, FAD2 and FAD3) and transcription factors (AP2 and C2H2) that regulate the metabolism of Camellia oil, especially for unsaturated fatty acids biosynthesis. Overall, the genomic resource generated from this study has great potential to accelerate the research for the molecular biology and genetic improvement of hexaploid oil-Camellia, as well as to understand polyploid genome evolution.