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Precise responses to changes in light quality are crucial for plant growth and development. For example, hypocotyls of shade‐avoiding plants typically elongate under shade conditions. Although this typical shade‐avoidance response (TSR) has been studied in Arabidopsis (Arabidopsis thaliana), the molecular mechanisms underlying shade tolerance are poorly understood. Here we report that B. napus (Brassica napus) seedlings exhibit dual shade responses. In addition to the TSR, B. napus seedlings also display an atypical shade response (ASR), with shorter hypocotyls upon perception of early‐shade cues. Genome‐wide selective sweep analysis indicated that ASR is associated with light and auxin signaling. Moreover, genetic studies demonstrated that phytochrome A (BnphyA) promotes ASR, whereas BnphyB inhibits it. During ASR, YUCCA8 expression is activated by early‐shade cues, leading to increased auxin biosynthesis. This inhibits hypocotyl elongation, as young B. napus seedlings are highly sensitive to auxin. Notably, two non‐canonical AUXIN/INDOLE‐3‐ACETIC ACID (Aux/IAA) repressor genes, BnIAA32 and BnIAA34, are expressed during this early stage. BnIAA32 and BnIAA34 inhibit hypocotyl elongation under shade conditions, and mutations in BnIAA32 and BnIAA34 suppress ASR. Collectively, our study demonstrates that the temporal expression of BnIAA32 and BnIAA34 determines the behavior of B. napus seedlings following shade‐induced auxin biosynthesis. [ABSTRACT FROM AUTHOR]

SUMMARY: Petals in rapeseed (Brassica napus) serve multiple functions, including protection of reproductive organs, nutrient acquisition, and attraction of pollinators. However, they also cluster densely at the top, forming a thick layer that absorbs and reflects a considerable amount of photosynthetically active radiation. Breeding genotypes with large, small, or even petal‐less varieties, requires knowledge of primary genes for allelic selection and manipulation. However, our current understanding of petal‐size regulation is limited, and the lack of markers and pre‐breeding materials hinders targeted petal‐size breeding. Here, we conducted a genome‐wide association study on petal size using 295 diverse accessions. We identified 20 significant single nucleotide polymorphisms and 236 genes associated with petal‐size variation. Through a cross‐analysis of genomic and transcriptomic data, we focused on 14 specific genes, from which molecular markers for diverging petal‐size features can be developed. Leveraging CRISPR‐Cas9 technology, we successfully generated a quadruple mutant of Far‐Red Elongated Hypocotyl 3 (q‐bnfhy3), which exhibited smaller petals compared to the wild type. Our study provides insights into the genetic basis of petal‐size regulation in rapeseed and offers abundant potential molecular markers for breeding. The q‐bnfhy3 mutant unveiled a novel role of FHY3 orthologues in regulating petal size in addition to previously reported functions. Significance Statement: Using a comprehensive analysis of genomic and transcriptomic data, this study proposes a set of 14 genes that can serve to develop molecular markers for diverging petal‐size features. These genes can also be potential targets for genetic manipulation aimed at reducing petal size. A q‐bnfhy3 mutant with reduced petal size was created, allowing for the validation of the previously unrecognized role of FHY3 orthologues in Brassica napus in the regulation of petal‐size formation. [ABSTRACT FROM AUTHOR]

Plant height, a key agronomic trait, affects crop structure, photosynthesis, and thus the final yield and seed quality. The combination of digital cameras on unmanned aerial vehicles (UAVs) and use of structure from motion have enabled high-throughput crop canopy height estimation. However, the focus of prior research has mainly been on plot-level height prediction, neglecting precise estimations for individual plants. This study aims to explore the potential of UAV RGB images with mask region-based convolutional neural network (Mask-RCNN) for high-throughput phenotyping of individual-level height (IH) in oilseed rape at different growth stages. Field-measured height (FH) of nine sampling plants in each subplot of the 150 subplots was obtained by manual measurement after the UAV flight. An instance segmentation model for oilseed rape with data augmentation based on the Mask-RCNN model was developed. The IHs were then used to obtain plot-level height based on individual-level height (PHIH). The results show that Mask-RCNN performed better than the conventional Otsu method with the F1 score increased by 60.8% and 26.6% under high and low weed pressure, respectively. The trained model with data augmentation achieved accurate crop height estimation based on overexposed and underexposed UAV images, indicating the model's applicability in practical scenarios. The PHIH can be predicted with the determination coefficient (r2) of 0.992, root mean square error (RMSE) of 4.03 cm, relative root mean square error (rRMSE) of 7.68%, which outperformed the results in the reported studies, especially in the late bolting stage. The IHs of the whole growth stages of oilseed can be predicted by this method with an r2 of 0.983, RMSE of 2.60 cm, and rRMSE of 7.14%. Furthermore, this method enabled a comprehensive Genome-wide association study (GWAS) in a 293-accession genetic population. The GWAS identified 200 and 65 statistically significant single nucleotide polymorphisms (SNPs), which were tightly associated with 28 and 11 candidate genes, at the late bolting and flowering stages, respectively. These findings demonstrated that the proposed method is promising for accurate estimations of IHs in oilseed rape as well as exploring the variations within the subplot, thus providing great potential for high-throughput plant phenotyping in crop breeding. [ABSTRACT FROM AUTHOR]

Nitrogen is essential for improving the seed oil yield of rapeseed (Brassica napus L.). However, the molecular mechanism by which increased nitrogen rates impact seed oil content is largely unknown. Therefore, a field experiment was conducted to determine how three nitrogen application rates (120, 240, and 360 kg ha−1) regulated seed oil content via transcriptomic analysis. The results showed that the seed yield and the protein and total N contents increased from N1 to N3, with average increases of 57.2%, 16.9%, and 79.5%, respectively. However, the seed oil content significantly decreased from N1 to N3, with an average decrease of 8.6%. These results were repeated over a number of years. The quantity of oil protein bodies observed under a transmission electron microscope was in accordance with the ultimate seed oil and protein contents. As the nitrogen application rate increased, a substantial number of genes involved in the photosynthesis, glycolysis, and phenylpropanoid biosynthesis pathways were up-regulated, as were TF families, such as AP2/ERF, MYB, and NAC. The newly identified genes were mainly involved in carbohydrate, lipid, and amino acid metabolism. Metabolic flux analysis showed that most of the genes involved in glycolysis and fatty acid biosynthesis had higher transcript levels in the early development stages. Our results provide new insights into the molecular regulation of rapeseed seed oil content through increased nitrogen application rates. [ABSTRACT FROM AUTHOR]

Tocopherols (Tocs) are a kind of lipid-soluble substance required for the normal physiological function of mammals, particularly their antioxidant capacity. Rapeseed (Brassica napus) oil is an important source of exogenous Tocs. However, the genotypic differences in the total Toc contents, the Toc composition in the seeds, and the molecular markers associated with the seed Toc remain largely unknown. Here, we selected 290 rapeseed accessions based on the resequencing of 991 genomes in a worldwide collection of rapeseed germplasm. The contents of the four Toc isoforms, namely, α-, β-, γ-, and δ-Tocs, were also measured. Results show that the total Toc content and the γ-/α-Toc ratio varied greatly across the accessions from 85.34 to 387.00 mg/mg and 0.65 to 5.03, respectively. Furthermore, we conducted genome-wide association studies on the Tocs, which identified 28 and 73 single nucleotide polymorphisms significantly associated with the variation of total Toc content and γ-/α-Toc ratio, respectively. Bna.C02.VTE4, a putative orthologue of Arabidopsis VITAMIN E DEFICIENT 4, was tightly associated with the γ-/α-Toc ratio. This study recommends specific genetic materials with particularly high total Toc and/or low γ-/α-Toc ratio and the molecular markers and haplotypes associated with these quality traits for rapeseed breeding. [ABSTRACT FROM AUTHOR]

Cuticular wax protects plants from various biotic and abiotic stresses. However, the genetic network of wax biosynthesis and the environmental factors influencing leaf wax production in rapeseed (Brassica napus) remains unclear. Here, we demonstrated the role of leaf wax in the resistance to Sclerotinia infection in rapeseed. We found that leaves grown under high light intensity had higher expression of genes involved in wax biosynthesis, and produced more wax on the leaf surface, compared with those grown under low light conditions. Genome-wide association study (GWAS) identified 89 single nucleotide polymorphisms significantly associated with leaf wax coverage. A cross-analysis between GWAS and differentially expressed genes (DEGs) in the leaf epidermis of the accessions with contrasting differences in wax content revealed 17 candidate genes that control this variation in rapeseed. Selective sweep analysis combined with DEG analysis unveiled 510 candidate genes with significant selective signatures. From the candidate genes, we selected BnaA02.LOX4 , a putative lipoxygenase, and BnaCnn.CER1 , BnaA02.CER3 , BnaC02.CER3 , and BnaA01.CER4 (ECERIFERUM1–4) that were putatively responsible for wax biosynthesis, to analyse the allelic forms and haplotypes corresponding to high or low leaf wax coverage. These data enrich our knowledge about wax formation, and provide a gene pool for breeding an ideal leaf wax content in rapeseed. [ABSTRACT FROM AUTHOR]

Oilseed rape (Brassica napus L.), an important oil crop of the world, suffers various abiotic stresses including salinity stress during the growth stage. While most of the previous studies paid attention to the adverse effects of high salinity stress on plant growth and development, as well as their underlying physiological and molecular mechanisms, less attention was paid to the effects of moderate or low salinity stress. In this study, we first tested the effects of different concentrations of NaCl solution on the seedling growth performance of two oilseed rape varieties (CH336, a semi-winter type, and Bruttor, a spring type) in pot cultures. We found that moderate salt concentrations (25 and 50 mmol L−1 NaCl) can stimulate seedling growth by a significant increase (10~20%, compared to controls) in both above- and underground biomasses, as estimated at the early flowering stage. We then performed RNA-seq analyses of shoot apical meristems (SAMs) from six-leaf-aged seedlings under control (CK), low (LS, 25 mmol L−1), and high (HS, 180 mmol L−1) salinity treatments in the two varieties. The GO and KEGG enrichment analyses of differentially expressed genes (DEGs) demonstrated that such a stimulating effect on seedling growth by low salinity stress may be caused by a more efficient capacity for photosynthesis as compensation, accompanied by a reduced energy loss for the biosynthesis of secondary metabolites and redirecting of energy to biomass formation. Our study provides a new perspective on the cultivation of oilseed rape in saline regions and new insights into the molecular mechanisms of salt tolerance in Brassica crops. The candidate genes identified in this study can serve as targets for molecular breeding selection and genetic engineering toward enhancing salt tolerance in B. napus. [ABSTRACT FROM AUTHOR]

Main Conclusion: Stomatal density and guard cell length of 274 global core germplasms of rapeseed reveal that the stomatal morphological variation contributes to global ecological adaptation and diversification of Brassica napus. Stomata are microscopic structures of plants for the regulation of CO2 assimilation and transpiration. Stomatal morphology has changed substantially in the adaptation to the external environment during land plant evolution. Brassica napus is a major crop to produce oil, livestock feed and biofuel in the world. However, there are few studies on the regulatory genes controlling stomatal development and their interaction with environmental factors as well as the genetic mechanism of adaptive variation in B. napus. Here, we characterized stomatal density (SD) and guard cell length (GL) of 274 global core germplasms at seedling stage. It was found that among the significant phenotypic variation, European germplasms are mostly winter rapeseed with high stomatal density and small guard cell length. However, the germplasms from Asia (especially China) are semi-winter rapeseed, which is characterized by low stomatal density and large guard cell length. Through selective sweep analysis and homology comparison, we identified several candidate genes related to stomatal density and guard cell length, including Epidermal Patterning Factor2 (EPF2; BnaA09g23140D), Epidermal Patterning Factor Like4 (EPFL4; BnaC01g22890D) and Suppressor of LLP1 (SOL1 BnaC01g22810D). Haplotype and phylogenetic analysis showed that natural variation in EPF2, EPFL4 and SOL1 is closely associated with the winter, spring, and semi-winter rapeseed ecotypes. In summary, this study demonstrated for the first time the relation between stomatal phenotypic variation and ecological adaptation in rapeseed, which is useful for future molecular breeding of rapeseed in the context of evolution and domestication of key stomatal traits and global climate change. [ABSTRACT FROM AUTHOR]

Summary: Plant genomes demonstrate significant presence/absence variation (PAV) within a species; however, the factors that lead to this variation have not been studied systematically in Brassica across diploids and polyploids. Here, we developed pangenomes of polyploid Brassica napus and its two diploid progenitor genomes B. rapa and B. oleracea to infer how PAV may differ between diploids and polyploids. Modelling of gene loss suggests that loss propensity is primarily associated with transposable elements in the diploids while in B. napus, gene loss propensity is associated with homoeologous recombination. We use these results to gain insights into the different causes of gene loss, both in diploids and following polyploidization, and pave the way for the application of machine learning methods to understanding the underlying biological and physical causes of gene presence/absence. [ABSTRACT FROM AUTHOR]

The utilization of heterosis is a successful strategy in increasing yield for many crops. However, it consumes tremendous manpower to test the combining ability of the parents in fields. Here, we applied the genomic-selection (GS) strategy and developed models that significantly increase the predictability of heterosis by introducing the concept of a regional parental genetic-similarity index (PGSI) and reducing dimension in the calculation matrix in a machine-learning approach. Overall, PGSI negatively affected grain yield and several other traits but positively influenced the thousand-seed weight of the hybrids. It was found that the C subgenome of rapeseed had a greater impact on heterosis than the A subgenome. We drew maps with overviews of quantitative-trait loci that were responsible for the heterosis (h-QTLs) of various agronomic traits. Identifications and annotations of genes underlying high impacting h-QTLs were provided. Using models that we elaborated, combining abilities between an Ogu-CMS-pool member and a potential restorer can be simulated in silico, sidestepping laborious work, such as testing crosses in fields. The achievements here provide a case of heterosis prediction in polyploid genomes with relatively large genome sizes. Author summary: Oilseed rape (Brassica napus) is of significant economic interest worldwide, providing high-quality oil with excellent health-promoting properties. It represents an excellent model of a successful recent polyploid that rapidly became an important crop worldwide. The utilization of hybridization, leading to hybrid vigor, or heterosis, is a successful strategy in increasing yield and vigor for many field crops including rapeseed (Brassica napus). However, the procedure of using classical breeding methods remains slow and laborious, illustrating the need for predictive and innovative methods. Here, we have achieved a significant breakthrough by using genome selection and significantly advanced models to predict the heterosis by pairing genome-wide nucleotides of parents. We provided maps with overviews of quantitative trait loci that were responsible for the heterosis of various agronomic traits. The research used deep resequencing (>30x) data of the entire polyploidy rapeseed genome, providing a successful case for the prediction of heterosis in polyploid genomes with relatively large genome sizes. Moreover, we provided the genetic information (SNPs) of 1007 core accessions of this species in the public domain for testing combinations with high heterosis using our predicting model for rapeseed breeders all over the world. [ABSTRACT FROM AUTHOR]

Rapeseed (Brassica napus L.) is a typical polyploid crop and one of the most important oilseed crops worldwide. With the rapid progress on high-throughput sequencing technologies and the reduction in sequencing cost, large-scale genomic data of a specific crop have become available. However, raw sequence data are mostly deposited in the sequence read archive of the National Center of Biotechnology Information and the European Nucleotide Archive, which is freely accessible to all researchers. Extensive tools for practical purposes should be developed to efficiently utilize these large raw data. Here, we report a web-based rapeseed genomic variation database (BnaGVD, http://rapeseed.biocloud.net/home) from which genomic variations, such as single-nucleotide polymorphisms (SNPs) and insertions/deletions (InDels) across a worldwide collection of rapeseed accessions, can be referred. The current release of the BnaGVD contains 34,591,899 high-quality SNPs and 12,281,923 high-quality InDels and provides search tools to retrieve genomic variations and gene annotations across 1,007 accessions of worldwide rapeseed germplasm. We implement a variety of built-in tools (e.g. BnaGWAS, BnaPCA and BnaStructure) to help users perform in-depth analyses. We recommend this web resource for accelerating studies on the functional genomics and the screening of molecular markers for rapeseed breeding. [ABSTRACT FROM AUTHOR]

Background: Transcription factors GATAs are involved in plant developmental processes and respond to environmental stresses through binding DNA regulatory regions to regulate their downstream genes. However, little information on the GATA genes in Brassica napus is available. The release of the reference genome of B. napus provides a good opportunity to perform a genome-wide characterization of GATA family genes in rapeseed. Results: In this study, 96 GATA genes randomly distributing on 19 chromosomes were identified in B. napus, which were classified into four subfamilies based on phylogenetic analysis and their domain structures. The amino acids of BnGATAs were obvious divergence among four subfamilies in terms of their GATA domains, structures and motif compositions. Gene duplication and synteny between the genomes of B. napus and A. thaliana were also analyzed to provide insights into evolutionary characteristics. Moreover, BnGATAs showed different expression patterns in various tissues and under diverse abiotic stresses. Single nucleotide polymorphisms (SNPs) distributions of BnGATAs in a core collection germplasm are probably associated with functional disparity under environmental stress condition in different genotypes of B. napus. Conclusion: The present study was investigated genomic structures, evolution features, expression patterns and SNP distributions of 96 BnGATAs. The results enrich our understanding of the GATA genes in rapeseed. [ABSTRACT FROM AUTHOR]

Summary: Plant‐based oils are valuable agricultural products, and seed oil content (SOC) is the major yield component in oil crops. Increasing SOC has been successfully targeted through the selection and genetic modification of oil biosynthesis. The SOC in rapeseed declined during the seed maturation and eventually caused the final accumulated seed oil quantity. However, genes involved in oil degradation during seed maturity are not deeply studied so far. We performed a candidate gene association study using a worldwide collection of rapeseed germplasm. We identified SEED FATTY ACID REDUCER (SFAR) genes, which had a significant effect on SOC and fatty acid (FA) composition. SFAR genes belong to the GDSL lipases, and GDSL lipases have a broad range of functions in plants. After quantification of gene expression using RNA‐seq and quantitative PCR, we used targeted (CRISPR‐Cas mediated) and random (chemical) mutagenesis to modify turnover rates of seed oil in winter rapeseed. For the first time, we demonstrate significant increase of SOC in a crop after knocking out members of the BnSFAR4 and BnSFAR5 gene families without pleiotropic effects on seed germination, vigour and oil mobilization. Our results offer new perspectives for improving oil yield by targeted mutagenesis. [ABSTRACT FROM AUTHOR]

Key message: We provided a gene pool of moderate size for selecting or manipulating the candidate genes that favour the acquisition of seed dormancy, shedding light on the elevation of seed oil content in oilseed rape by blocking lipid degradation in developing seeds. In oilseed rape, the association between the germination potential of premature seeds and the final level of seed lipids, and the underlying mechanism, is elusive. Here, we investigated phenotypic differences in the germination percentage of premature seeds in a collection of oilseed rape cultivars. We compared the dynamic lipid accumulation between the deep-, moderate- and non-dormant genotypes and compared the transcriptomes of the seeds at 40 days after pollination between multiple pairs of deep- and non-dormant genotypes. We identified a wide range of differences in germination percentage of premature seeds and the association between the germination potential and the change of fatty acid content at late stage of seed maturation. The comparisons of transcriptomes between deep- and non-dormant seeds revealed the genetic basis for the dormant difference, e.g. the different expression levels of the genes involved in gibberellic and abscisic acid biosynthesis and/or signalling, fatty acid metabolic pathways, and the structure of seed cell wall. We provided a gene pool of moderate size for selecting or manipulating the candidate genes that favour the acquisition of seed dormancy, shedding light on the elevation of seed oil content in oilseed rape by blocking lipid degradation in developing seeds. [ABSTRACT FROM AUTHOR]

Background: Sucrose non-fermenting 1 related protein kinases (SnRK) play crucial roles in responding to biotic and abiotic stresses through activating protein phosphorylation pathways. However, little information of SnRK genes was available in Brassica napus, one of important oil crops. Recently, the released sequences of the reference genome of B.napus provide a good chance to perform genome-wide identification and characterization of BnSnRK gene family in the rapeseed. Results: Totally 114 SnRK genes distributed on 19 chromosomes were identified in the genome of B.napus and classified into three subfamilies on the basis of phylogenetic analysis and the domain types. According to gene structure and motif composition analysis, the BnSnRK sequences showed obvious divergence among three subfamilies. Gene duplication and synteny between the genomes of the rapeseed and Arabidopsis were also analyzed to provide insights into the evolutionary characteristics of BnSnRK family genes. Cis-element analysis revealed that BnSnRKs may response to diverse environmental stresses. Moreover, the expression patterns of BnSnRKs in various tissues and under diverse abiotic stresses were distinct difference. Besides, Single Nucleotide Polymorphisms (SNP) distribution analysis suggests the function disparity of BnSnRK family genes in different genotypes of the rapeseed. Conclusion: We examined genomic structures, evolution features, expression patterns and SNP distribution of 114 BnSnRKs. The results provide valuable information for functional characterization of BnSnRK genes in future studies. [ABSTRACT FROM AUTHOR]

Efficient molecular markers for the selection of rapeseed genetic materials with high seed oil content and ideal fatty acid (FA) composition are preferred by rapeseed breeders. Recently, we reported the molecular mechanism of TRANSPARENT TESTA 2 (TT2) in inhibiting seed FA biosynthesis in Arabidopsis. However, evidence showing the association of rapeseed TT2 homologs and seed FA production are still insufficient. In this study, we collected 83 rapeseed (Brassica napus L.) landraces from different geographical backgrounds to conduct association mapping of BnaC.TT2.a in relation to seed coat color and FA biosynthesis. Population background was corrected by 84 pairs of SSR markers that were uniformly distributed among the linkage groups of the Tapidor-Ningyou-7 DH population. A single copy of BnaC.TT2.a for single nucleotide polymorphism (SNP) assay was cloned by a pair of previously reported specific primers. From the analysis of BnaC.TT2.a allelic variations using GLM+Q model, four SNPs on intron 1 of BnaC.TT2.a that were associated with seed FA were discovered. Moreover, an InDel at position 738 on exon 3 of BnaC.TT2.a indicated a change of protein function that was significantly associated with seed coat color, linoleic acid (C18:2), and total FA content. These findings revealed the role of BnaC.TT2.a in regulating the seed color formation and seed FA biosynthesis in rapeseed, thereby suggesting effective molecular markers for rapeseed breeding. [ABSTRACT FROM AUTHOR]

Seed oil production in oilseed rape is greatly affected by the temperature during seed maturation. However, the molecular mechanism of the interaction between genotype and temperature in seed maturation remains largely unknown. We developed two near-isogenic lines (NIL-9 and NIL-1), differing mainly at a QTL region influencing oil content on Brassica napus chromosome C2 ( qOC.C2.2) under high temperature during seed maturation. The NILs were treated under different temperatures in a growth chamber after flowering. RNA from developing seeds was extracted on the 25th day after flowering (DAF), and transcriptomes were determined by microarray analysis. Statistical analysis indicated that genotype, temperature, and the interaction between genotype and temperature (G × T) all significantly affected the expression of the genes in the 25 DAF seeds, resulting in 4,982, 19,111, and 839 differentially expressed unisequences, respectively. NIL-9 had higher seed oil content than NIL-1 under all of the temperatures in the experiments, especially at high temperatures. A total of 39 genes, among which six are located at qOC.C2.2, were differentially expressed among the NILs regardless of temperature, indicating the core genetic divergence that was unaffected by temperature. Increasing the temperature caused a reduction in seed oil content that was accompanied by the downregulation of a number of genes associated with red light response, photosynthesis, response to gibberellic acid stimulus, and translational elongation, as well as several genes of importance in the lipid metabolism pathway. These results contribute to our knowledge of the molecular nature of QTLs and the interaction between genotype and temperature. [ABSTRACT FROM AUTHOR]

In this study, we performed a transcriptomic analysis to investigate genome-wide gene profiles of a rapeseed (Brassica napus) cultivar Zhongshuang 11 (ZS11) in response to waterlogging stress at germination stage. The root and shoot development of ZS11 was dramatically inhibited by waterlogging stress. As a result, 7472 downregulated DEGs (differentially expressed genes) and 3869 upregulated DEGs were identified by the RNA-seq experiments. KEGG analyses show that enriched pathways of these DEGs mainly include "plant hormone signal transduction," "phenylpropanoid biosynthesis," and "starch and sucrose metabolism." Among them, there are 41, 19, and 26 DEGs involved in the regulatory pathways of root, shoot, and hypocotyl growth, respectively. In detail, the downregulated IAA17, IAA28, YUCCA9, UPBEAT1, and ARR1 and the upregulated ACR4 probably affect the balance between cell differentiation and division in the root apical meristem (RAM), while the downregulated CLV1, CRN, AHK4, and FAS2 might disturb stem cell fate in the shoot apical meristem (SAM). Taken together, the current results provide valuable information for understanding molecular mechanisms of seedling development in response to waterlogging stress at germination stage in rapeseed. [ABSTRACT FROM AUTHOR]