Woody Oil Crop Research Articles

Transcriptome and miRNA Reveal the Key Factor Regulating the Somatic Embryogenesis of Camellia oleifera

The key genes involved in plant regeneration play a crucial role in enhancing reproductive capabilities, plant genetic transformation, and gene editing efficiency. Camellia oleifera, a vital woody oil crop, faces challenges in genetic improvement efficiency due to its slow growth and the difficulties it experiences during the regeneration process. This study focused on the expression levels of mRNA and miRNA during the somatic embryogenesis of C. oleifera, and the core genes of plant regeneration involved in the C. oleifera somatic embryogenesis process were identified, including WUSCHEL-related homeobox 4 (WOX4), WOX13, and DNA-Binding One Zinc Finger 5.6 (DOF5.6) during the somatic embryo callus induction phase; WOX11, PLETHORA2 (PLT2), and Growth-regulating factor (GRF) during the somatic embryogenesis and bud regeneration phase; and miRNAs such as miR156, miR319, and miR394. These key regulatory factors may participate in the regulation of plant auxin and cytokinin and play a core role in the regeneration process of C. oleifera. The research data elucidate the process of somatic embryogenesis in C. oleifera at the molecular level. The key regulatory genes identified provide potential targets for improving the regeneration efficiency of C. oleifera and other woody oilseed plants.

Metabolite Analysis of Camellia oleifera Fruit Pericarp Using UPLC-MS/MS: A Comparative Study of Three Oil Tea Varieties.

Camellia oleifera, a widely cultivated woody oil crop, holds economic significance because of its ability to grow without encroaching on cultivated land. The pericarp of C. oleifera is abundant in flavonoids and phenolic acids, which offer significant nutritional benefits. This study used metabolomic technology (UPLC-ESI-MS/MS) to discern metabolite variances in the pericarp of three C. oleifera types (COT, BFOT, and SFOT) during the maturity stage and subsequently analyzed and compared them. A total of 1117 metabolites were detected in the study, including 277 flavonoids, 221 phenolic acids, 108 lipids, 93 amino acids and their derivatives, 83 organic acids, 59 nucleotides and their derivatives, 57 alkaloids, 52 lignans, 44 tannins, 23 terpenoids, and 100 miscellaneous metabolites (such as sugars, alcohols, vitamins, and other unclassified substances). Clustering and PCA analyses revealed distinct separation of COT, BFOT, and SFOT, indicating variances in metabolites within the pericarp peels of these three C. oleifera types. KEGG enrichment analysis demonstrated that 143 shared differential metabolites were primarily associated with amino acid biosynthesis. These findings are expected to significantly enhance the current knowledge of the C. oleifera pericarp and pave the way for future development and use efforts.

Metabolome and Transcriptome Analyses Reveal Metabolomic Variations and Key Transcription Factors Involved in Lipid Biosynthesis During Seed Development in Carya illinoinensis.

Plant oils are a large group of neutral lipids that play a vital role in the food and oleochemical industries. The pecan (Carya illinoinensis) is a promising woody oil crop known for its high-quality sources of essential fatty acids and various bioactive compounds that may aid in preventing heart diseases. However, there is still a lack of understanding regarding the accumulation of lipids and the molecular mechanism of lipid biosynthesis during seed development. This study aims to analyze the metabolite variations and molecular mechanisms of lipid biosynthesis by integrating untargeted metabolomics and transcriptomics during pecan seed development. A total of 293 differentially accumulated metabolites were identified and further categorized into 13 groups, with lipids and lipid-like molecules constituting the largest group. The oil content and fatty acid compositions of pecan embryos were assessed at three stages of seed development. Oleic acid (c18:1) and linoleic acid (c18:2n6) were found to be the most abundant unsaturated fatty acid components in pecan embryos. Additionally, a comprehensive analysis revealed 15,990 differentially expressed genes, with a focus on the key genes related to lipid metabolism. Furthermore, the study identified 1201 transcription factors from differentially expressed genes. These transcription factors were divided into 65 families, with different members in the same family exhibiting different expression patterns during seed development. The expression patterns of ten transcription factor genes during seed development were verified by qRT-PCR. Two key genes, CiABI3 and CiFUS3 were further cloned and found to be localized in the nucleus. This study used metabolome and transcriptome analysis during key periods of pecan seed development to identify the key genes associated with seed development and fatty acid biosynthesis.

Progress in the resistance mechanism and breeding of Camellia oleifera with resistance to anthracnose

Camellia oleifera is an important woody oil crop in China, and its seed oil has a high economic value. Anthracnose, one of the main diseases in C. oleifera, occurs in a wide range in the production areas, limiting the growth and development of plants and causing serious losses of oil production. With the rapid development of the C. oleifera industry in recent years, great progress has been achieved in the research on anthracnose in C. oleifera. This paper summarized the resistance mechanisms, the mining of resistance genes, and the evaluation of resistant germplasm resources, aiming to provide a theoretical basis for the prevention and control of anthracnose and the breeding of C. oleifera germplasm with resistance to anthracnose.

Single Nucleotide Polymorphisms and Insertion/Deletion Variation Analysis of Octoploid and Decaploid Tropical Oil Tea Camellia Populations Based on Whole-Genome Resequencing.

Oil tea camellia (Camellia spp.) is an important woody oil crop with a high nutritional and economic value. Whole-genome resequencing (WGR) technology can provide an in-depth understanding of the genetic background of this plant as well as a reference for breeding research, germplasm resource conservation, and genetic modification. In this study, we analyzed SNP and InDel variations in 49 individual oil tea camellia germplasm samples collected from five populations located in three provinces of China: Hainan, Guangdong and Guangxi. The samples were analyzed through WGR after the ploidy of the samples was determined through flow cytometry. A total of 239,441,603 high-quality single nucleotide polymorphisms (SNPs) and 23,510,374 high-quality insertion/deletion variation sites (InDels) were obtained. The distribution of SNPs and InDels in different functional regions differed significantly, with a high density of variations in non-coding regions, such as intergenic regions and introns, and a relatively low density of variations in coding regions. Transition was the main type of SNP variation. A population genetic diversity analysis revealed that the sampled oil tea camellia populations exhibited a high genetic diversity and extensive genetic variation. The genetic diversity of the oil tea camellia populations in the Hainan region was higher than inland regions. This study also determined the genetic diversity of and variations between octoploid and decaploid oil tea camellia in the tropics and between Hainan-based and inland oil tea camellia. Such findings provide a reference for the conservation of germplasm resources and the genetic modification of oil tea camellia.

Screening 60Co-γ Irradiated Camellia oleifera Lines for Anthracnose-Resistant

Camellia oleifera C. Abel is a woody oil crop with multiple purposes. This study aims to investigate the mutagenic effects of 60Co-γ radiation on C. oleifera seedlings and to screen anthracnose-resistant mutants. Two C. oleifera varieties were investigated: ‘Xianglin 1’ (XL1) and ‘Xianglin 210’ (XL210). Seeds were irradiated with 0 Gy, 30 Gy, 50 Gy, and 80 Gy of 60Co-γ, and after one year of planting, the mutagenic lines were studied, and disease-resistant mutants were screened. Results showed that as the radiation intensity was increased, the emergence percentage of both C. oleifera XL210 and XL1 was significantly decreased. Radiation significantly changed the SOD and POD activities in both varieties. Furthermore, 80 Gy irradiated lines showed reduced anthracnose resistance in both varieties. However, 50 Gy irradiated lines showed enhanced disease resistance in XL210 while reducing it in XL1. The 30 Gy irradiated lines did not affect the disease resistance of either variety. Colletotrichum gloeosporioides infection tests were conducted on 94 mutant C. oleifera seedlings, resulting in 8 highly resistant mutants (A3, A8, A10, A19, A21, A32, A35, B17) and 3 susceptible mutants (A4, B15, B27) in XL210 and XL1. Differences in SOD and POD activities led to variations in disease resistance among different mutants. Additionally, the expression levels of CoSOD1, CoPOD, CoIDD4, and CoWKRY78 were varied among the different mutants. This study delivers the screening of disease-resistant mutants in C. oleifera through mutagenic breeding, providing material for the development of new C. oleifera varieties and serving as a resource for further research in mutagenic breeding.

Functional Characterization of the Paeonia ostii P5CS Gene under Drought Stress.

With persistent elevation in global temperature, water scarcity becomes a major threat to plant growth and development, yield security, agricultural sustainability, and food production. Proline, as a key osmolyte and antioxidant, plays a critical role in regulating drought tolerance in plants, especially its key biosynthetic enzyme, delta-1-pyrroline-5-carboxylate synthase (P5CS), which always positively responds to drought stress. As an important woody oil crop, the expansion of Paeonia ostii cultivation needs to address the issue of plant drought tolerance. Here, we isolated a PoP5CS gene from P. ostii, with an open reading frame of 1842 bp encoding 613 amino acids. PoP5CS expression progressively increased in response to increasing drought stress, and it was localized in the cytoplasm. Silencing of PoP5CS in P. ostii reduced drought tolerance, accompanied by decreased proline content, elevated reactive oxygen species (ROS) accumulation, and increased relative electrical conductivity (REC) and malondialdehyde (MDA) levels. Conversely, overexpression of PoP5CS in Nicotiana tabacum plants enhanced drought resistance, manifested by increased proline levels, reduced ROS accumulation, and lower REC and MDA contents. This study isolates PoP5CS from P. ostii and validates its role in regulating drought tolerance, providing valuable genetic resources and theoretical insights for the development of drought-resistant P. ostii cultivars.

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.

Single-nucleotide polymorphisms and copy number variations drive adaptive evolution to freezing stress in a subtropical evergreen broad-leaved tree: Hexaploid wild Camellia oleifera

Subtropical evergreen broad-leaved trees are usually vulnerable to freezing stress, while hexaploid wild Camellia oleifera shows strong freezing tolerance. As a valuable genetic resource of woody oil crop C. oleifera, wild C. oleifera can serve as a case for studying the molecular bases of adaptive evolution to freezing stress. Here, 47 wild C. oleifera from 11 natural distribution sites in China and 4 relative species of C. oleifera were selected for genome sequencing. “Min Temperature of Coldest Month” (BIO6) had the highest comprehensive contribution to wild C. oleifera distribution. The population genetic structure of wild C. oleifera could be divided into two groups: in cold winter (BIO6 ≤ 0 °C) and warm winter (BIO6 > 0 °C) areas. Wild C. oleifera in cold winter areas might have experienced stronger selection pressures and population bottlenecks with lower Ne than those in warm winter areas. 155 single-nucleotide polymorphisms (SNPs) were significantly correlated with the key bioclimatic variables (106 SNPs significantly correlated with BIO6). Twenty key SNPs and 15 key copy number variation regions (CNVRs) were found with genotype differentiation > 50% between the two groups of wild C. oleifera. Key SNPs in cis-regulatory elements might affect the expression of key genes associated with freezing tolerance, and they were also found within a CNVR suggesting interactions between them. Some key CNVRs in the exon regions were closely related to the differentially expressed genes under freezing stress. The findings suggest that rich SNPs and CNVRs in polyploid trees may contribute to the adaptive evolution to freezing stress.

Variation in Fruit Traits and Seed Nutrient Compositions of Wild Camellia oleifera: Implications for Camellia oleifera Domestication

Camellia oleifera is a woody oil crop with the highest oil yield and the largest cultivation area in China, and C. oleifera seed oil is a high-quality edible oil recommended by the Food and Agriculture Organization of the United Nations. The objectives of this study were to investigate the variation in fruit yield traits and seed chemical compositions of wild C. oleifera in China and to identify the differences between wild C. oleifera and cultivated varieties. In this study, we collected wild C. oleifera samples from 13 sites covering the main distribution areas of wild C. oleifera to comprehensively evaluate 25 quantitative traits of wild C. oleifera fruit and seed chemical compositions and collected data of 10 quantitative traits from 434 cultivated varieties for a comparative analysis of the differences between wild and cultivars. The results showed that the coefficients of variation of the 25 quantitative traits of wild C. oleifera ranged from 2.605% to 156.641%, with an average of 38.569%. The phenotypic differentiation coefficients ranged from 25.003% to 99.911%, with an average of 77.894%. The Shannon–Wiener index (H’) ranged from 0.195 to 1.681. Based on the results of principal component analysis (PCA) and phenotypic differentiation coefficients, 10 traits differed significantly between wild C. oleifera and cultivated varieties, while the differentiation coefficients (VST) for fresh fruit weight, oleic acid, unsaturated fatty acids, stearic acid, and saturated fatty acids were more than 95%, of which fresh fruit weight and oleic acid content were potential domestication traits of C. oleifera. The results of this study can contribute to the efficient excavation and utilization of wild C. oleifera genetic resources for C. oleifera breeding.

A Set of Artificial Pollination Technical Measures: Improved Seed Yields and Active Ingredients of Seeds in Oil Tree Peonies.

The tree peony, a novel woody oil crop extensively cultivated in China, necessitates further investigation into artificial pollination technology to enhance seed yield. In this study, we conducted artificial pollination experiments with 6-year-old Paeonia ostii 'Feng Dan' seedings for suitable pollen sources, pollen concentration, pollination timing, and pollination frequency. By evaluating seed yields, active ingredients, and oil quality, we derived the following significant conclusions. Firstly, compared to natural pollination, artificial pollination could significantly increase the fruit diameter by 13.94-27.58%, seed yields by 35.17-58.99%, and oil content by 6.45-7.52% in tree peonies. In active ingredients, seeds produced by pollen from Hantai County significantly enhanced starch content (by 48.64%), total phenols (by 41.18%) and antioxidant capacity (by 54.39%). In oil quality, seeds produced by pollen from Heyang County exhibited the highest α-linolenic acid and total fatty acid content with enhancements of 1.68%, 7.41%, and 8.48%. Secondly, hand pollination with pure pollen significantly increased seed yield by 58.99%, total phenol content by 40.97%, antioxidant capacity by 54.39%, and oil content by 1.53% compared to natural pollination. Thirdly, pollination at 2/3 bloom range significantly increased seed number by 63.08% and yield by 45.61% compared to natural pollination. Finally, the effect of one, two, and three pollination events had no difference in seed yield. So, to summarize, applying a 100% concentration of allochthonous pollen once is recommended when the bloom range is more than two thirds.

Bumblebee pollination ensures the stability of both yield and quality of the woody oil crop Paeonia ostii ‘Fengdan’

Oil tree peony is a unique woody oil crop found exclusively in China. Its seed oil is a highly nutritious edible vegetable oil. However, its seed production varies greatly and is often low. Oil tree peony is a plant that relies on insects for pollination, but inadequate pollination is a common occurrence. In this study, we focused on the Paeonia ostii ‘Fengdan’ species and conducted a five-year study (from 2017 to 2022) in Luoyang, China. Our objective was to assess the extent of pollination deficiency and dependence, as well as quantify the contribution of supplemented bumblebees (Bombus terrestris) to the yield of oil tree peony. We also examined the effect of supplemented bumblebees on the temporal variation in yield through various pollinator survey designs, including supplemented bumblebees (BP), open pollination (OP), pollinator exclusion (EP), self-pollination treatments (SP), and artificial cross-pollination (CP). The results revealed a medium pollination deficit (D = 0.50) at the study sites for three consecutive years from 2020 to 2022, indicating limited pollination for oil tree peony under natural conditions. Importantly, BP significantly compensated for this deficiency (D = 0.22). Over the course of five years, BP increased the yield of oil tree peony by 82.87% on average compared to EP. Furthermore, the yield variation coefficient of EP (CVt=0.20) increased by 100% compared to BP (CVt=0.10). And we also observed significant variability in other yield parameters. Additionally, oil tree peony production was reduced by 44.24% in the absence of flower visitors, and the dependence on BP reached a “high” level. The fatty acid content in the seed oil did not show significant differences across treatments, indicating its stability. Overall, our pollination practices demonstrate that supplementing bee pollination can provide sufficient and stable pollination services, resulting in a higher and more stable yield of oil tree peony seeds.

Single-cell RNA-seq reveals a link of ovule abortion and sugar transport in Camellia oleifera.

Camellia oleifera is the most important woody oil crop in China. Seed number per fruit is an important yield trait in C. oleifera. Ovule abortion is generally observed in C. oleifera and significantly decreases the seed number per fruit. However, the mechanisms of ovule abortion remain poorly understood at present. Single-cell RNA sequencing (scRNA-seq) was performed using mature ovaries of two C. oleifera varieties with different ovule abortion rates (OARs). In total, 20,526 high-quality cells were obtained, and 18 putative cell clusters were identified. Six cell types including female gametophyte, protoxylem, protophloem, procambium, epidermis, and parenchyma cells were identified from three main tissue types of ovule, placenta, and pericarp inner layer. A comparative analysis on scRNA-seq data between high- and low-OAR varieties demonstrated that the overall expression of CoSWEET and CoCWINV in procambium cells, and CoSTP in the integument was significantly upregulated in the low-OAR variety. Both the infertile ovule before pollination and the abortion ovule producing after compatible pollination might be attributed to selective abortion caused by low sugar levels in the apoplast around procambium cells and a low capability of hexose uptake in the integument. Here, the first single-cell transcriptional landscape is reported in woody crop ovaries. Our investigation demonstrates that ovule abortion may be related to sugar transport in placenta and ovules and sheds light on further deciphering the mechanism of regulating sugar transport and the improvement of seed yield in C. oleifera.

Research progress of woody oil crops in China: a review

Research progress of woody oil crops in China: a review

Physiological and Transcriptional Analysis Provides Insights into Tea Saponin Biosynthesis and Regulation in Response to SA in Camellia vietnamensis Huang

Camellia vietnamensis Huang is an important and famous woody oil crop with high economic value in China because of its high-quality, edible, and medicinal oil. As one of its major active components, tea saponin (triterpenoid saponin) has shown anticancer, antioxidant, bacteriostatic, and other pharmacological activities. In this study, C. vietnamensis was used as an experimental material to determine the tea saponin content and physiological activity indicators after salicylic acid (SA) treatment and to analyze the differential expression genes of key metabolic pathways in response to SA by combining transcriptome data. The results showed that SA treatment increased the content of tea saponin and total phenols in leaves; effectively promoted the activity of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX); and decreased the content of malondialdehyde (MDA). A total of 60,038 genes, including 5871 new genes, were obtained by the RNA-seq. There were 6609 significantly differential expression genes mainly enriched in pathways such as sesquiterpenoid and triterpenoid biosynthesis, terpenoid backbone biosynthesis, diterpenoid biosynthesis, and flavonoid biosynthesis. The SA-induced key structural genes (SQS, SQE, bAS, CYP450, and UGT) and transcription factors related to the tea saponin biosynthetic pathway were screened by weighted gene co-expression network analysis (WGCNA). The results of this study could provide a theoretical basis and a new technical method to improve the content of tea saponin, with its excellent anticancer activity, in C. vietnamensis.

The Application of Nitrogen, Phosphorus, and Potassium Regulate the Growth and Morphological Development of Torreya grandis (Taxaceae) Saplings

Torreya grandis Fort. ex Lindl. cv. “Merrillii” is an important woody oil crop, and the development of plantations relies on the cultivation of high-quality saplings. For this study, 6-year-old grafted T. grandis saplings, which will soon be planted on the mountain, were selected to investigate the regulatory effects of nitrogen (N), phosphorus (P), and potassium (K) on their growth and morphology. To determine the optimal dosage and ratio of N–P–K fertilizer for sapling cultivation, we employed a three-factor four-level L16 (43) orthogonal experiment design. The experiment included a total of 17 treatments—a control group where no fertilizer was applied and 16 treatments with varying levels of NPK supply. We conducted a one-season experiment under a prescribed fertilizer regime and measured root collar diameters and sapling heights, the root, shoot, leaf biomass, total biomass, and the nutritional status of plant organs (root, shoot, leaf). From these measurements, we calculated the root–shoot ratio (RS) and seedling quality index (QI). The application of N–P–K fertilizer exhibited significant benefits for T. grandis sapling cultivation, promoted their growth and biomass accumulation and altered the nutrient allocation patterns in organs. Ultimately, we determined the ideal N–P–K ratio for T. grandis growth to be 1:0.46:0.75, with a fertilizer application of 1.38 g·sapling−1 of N, 0.64 g·sapling−1 of P (P2O5), and 1.04 g·sapling−1 of K (K2O).

Genome survey and identification of key genes associated with freezing tolerance in genomic draft of hexaploid wild Camellia oleifera

ABSTRACT Camellia oleifera Abel. is the dominant woody oil crop under significant development in China. Wild C. oleifera in Lu Mountain is a valuable genetic resource with strong freezing tolerance. With high-throughput sequencing, the genome of wild C. oleifera in Lu Mountain was analysed and 700.3 Gb clean reads were obtained. The genome of wild C. oleifera was estimated as allohexaploid, and its haplotype genome size was about 2.69 Gb-2.79 Gb, with repeat content of 63.01%-73.02% and heterozygosity of 6.30%-7.43%, belonging to a very complex genome. The genomic draft was assembled that contained a total of 6,952,303 scaffolds with N50 length of 1.23 kb, and the overall length was 2.39 Gb with GC content of 40.87%. In the genomic draft, 1,104,618 SSRs were identified; scaffold1096012 and scaffold1779458 were identified as key genes associated with freezing tolerance combined with the transcriptome data of field plus lab experiments. In this study, the genomic background of hexaploid wild C. oleifera in Lu Mountain was revealed. This lays the foundation for obtaining the high-quality chromosome-level reference genome of wild C. oleifera. The identification of SSRs and key genes associated with freezing tolerance may contribute to the efficient exploration and utilisation of this genetic resource.

Efficacy mechanisms research progress of the active components in the characteristic woody edible oils

AbstractWoody edible oils are a type of vegetable oil. Woody edible oils like olive oil have greater quantities of unsaturated fatty acids (UFAs), particularly essential FAs, as well as vitamin E, phytosterols, and other nutrients that are becoming more vital in human health. As a result, finding high‐quality woody oil resource plants is critical to ensuring enough edible oil supply. As six novel woody crops, Paeonia suffruticosa, Plukenetia volubilis, Acer truncatum, Olea europaea, Camellia sinensis, and Camellia oleifera are characterized by high oil production, widespread cultivation, adaptability, and various active ingredients. The six woody crop oils contain UFAs (e.g., α‐linolenic acid, oleic acid, and linoleic acid), vitamin E, polyphenols, phytosterols, and so forth. The presence of these active ingredients confers anti‐inflammatory, antioxidant, cholesterol and lipid metabolism regulating, blood lipid lowering, immune boosting, memory improving, intestinal flora regulating, and other properties to the oils, which are beneficial to body health. This article examined in depth the seed resources, FA composition, active component kinds, active ingredient efficacy mechanism, and physiological impacts of these six novel woody crop oils. These developments lay a solid platform for further study and development of these woody oil crops.

Transcriptomic Time-Course Sequencing: Insights into the Cell Wall Macromolecule-Mediated Fruit Dehiscence during Ripening in Camellia oleifera.

Camellia oleifera (C. oleifera), one of the world's four major edible woody oil crops, has been widely planted in southern China's subtropical region for the extremely high nutritional and health benefits of its seed oil. Timing and synchronization of fruit dehiscence are critical factors influencing the oil output and quality, as well as the efficiency and cost of harvesting C. oleifera, yet they extremely lack attention. To gain an understanding of the molecular basis underlying the dehiscence of C. oleifera fruit, we sampled pericarp-replum tissues containing dehiscence zones from fruits at different developmental stages and performed time-series transcriptomic sequencing and analysis for the first time. Statistical and GO enrichment analysis of differentially expressed genes revealed that drastic transcriptional changes occurred over the last short sampling interval (4 days, 18th-22nd October), which directed functional classifications link to cell wall and cell wall macromolecule activity. WGCNA further showed that factors controlling cell wall modification, including endo-1,3;1,4-beta-D-glucanase, WAT1-like protein 37, LRR receptor-like serine/threonine-protein kinase, and cellulose synthase A catalytic subunit, were identified as core members of the co-expression network of the last stage highly related modules. Furthermore, in these modules, we also noted genes that were annotated as coding for polygalacturonase and pectinesterase, two pectinases that were expected to be major players in cell separation during dehiscence. qRT-PCR further confirmed the expression profiles of these cell wall modification relating factors, which possessed a special high transcriptional abundance at the final stage. These results suggested the cell wall associated cell separation, one of the essential processes downstream of fruit dehiscence, happened in dehiscing fruit of C. oleifera during ripening. Hydrolases acting on cell wall components are good candidates for signal mediating dehiscence of C. oleifera fruit. In conclusion, our analysis provided insights into the cell wall macromolecule-mediated fruit dehiscence during ripening in C. oleifera.

Optimization of In Vitro Germination, Viability Tests and Storage of Paeonia ostii Pollen.

Paeonia ostii is an important woody oil crop mainly cross-pollinated. However, the low yield has become an important factor restricting the industrial development of P. ostii. Cross-pollination has become one of the important measures to increase the seed yield. Therefore, conservation of pollen with high vitality is crucial to ensure successful pollination of P. ostii. In this study, we found an effective methodological system to assess the viability, ability to germinate, and optimal storage conditions of P. ostii pollen grains. The optimal medium in vitro was 50 g/L sucrose, 100 mg/L boric acid, 50 g/L PEG6000, 100 mg/L potassium nitrate, 300 mg/L calcium nitrate, and 200 mg/L magnesium sulfate at pH 5.4. Optimal germination condition in vitro was achieved at 25 °C for 120 min, allowing easy observation of the germination percentage and length of the pollen tubes. In addition, the viability of pollen grains was assessed by comparing nine staining methods. Among them, MTT, TTC, benzidine-H2O2, and FDA were effective to distinguish between viable and non-viable pollen, and the results of the FDA staining method were similar to the pollen germination percentage in vitro. After evaluation of pollen storage, thawing and rehydration experiments showed that thawing at 4 °C for 30 min and rehydration at 25 °C for 30 min increased the germination percentage of pollen grains stored at low temperatures. The low-temperature storage experiments showed that 4 °C was suitable for short-term storage of P. ostii pollen grains, while -80 °C was suitable for long-term storage. This is the first report on the in vitro germination, viability tests, and storage of P. ostii pollen grains, which will provide useful information for P. ostii germplasm conservation and artificial pollination.