Genome-Wide Association Analysis Combined With Quantitative Trait Loci Mapping and Dynamic Transcriptome Unveil the Genetic Control of Seed Oil Content in Brassica napus L

The Alpha/Beta-Hydrolase Fold Superfamily in Brassica napus: Expression Profiles and Functional Implications of Clade-3 BnABH Proteins in Response to Abiotic Stress

Alpha/beta hydrolase (ABHs) fold esterase/lipase proteins represent a prominent family within the serine hydrolase (SH) superfamily that includes esterases and lipases and other catalytic and non-catalytic proteins. ABHs play crucial roles in both the fundamental and secondary metabolic pathways, including the synthesis and degradation of triacylglycerols (TAGs), key components of plant oils. Despite their importance in oil production, the ABH gene family in the oil crop Brassica napus has not been comprehensively analyzed. In the present study, we identified 777 BnABH genes in the B. napus cultivar 'Zhongshuang 11' (ZS11). Phylogenetic analysis categorized these BnABH genes into 10 distinct groups. Twenty-four BnABHs were identified through esterase activity staining and mass spectrometry, 11 of which were classified into clade C3. Examination of the gene and protein structures, expression patterns, and cis-elements of the BnABHs in clade C3 suggested diverse functional roles across different tissues and in response to various environmental stresses. In particular, BnABH205 was highly induced by high temperatures. Subcellular localization analysis revealed that the BnABH205 protein was localized to the plastid. Further analysis revealed five haplotypes within the coding and 3' untranslated regions of BnABH205 that were significantly associated with seed oil content (SOC). Overall, this study provides a comprehensive understanding of BnABHs and introduces a robust methodology for identifying potential esterase/lipase genes that regulate seed oil content (SOC) in response to environmental hazards, especially heat waves during seed maturation.

Integrating QTL mapping and GWAS to decipher the genetic mechanisms behind the calcium contents of Brassica napus shoots

Brassica napus is an important oil crop worldwide, and its shoots are rich in vitamin C, calcium, and selenium. Functional oilseed-vegetable-dual-purpose varieties can increase the subsidiary value of B. napus. Consumption of high-calcium B. napus shoots can effectively help provide essential elements to the human body. To investigate the genetic mechanisms underlying the calcium concentrations of B. napus shoots, quantitative trait loci (QTL) mapping, using a population of 189 recombinant inbred lines, and a genome-wide association study, using an association panel of 202 diverse accessions, were performed. A total of 12 QTLs controlling calcium content were identified using the recombinant inbred line population in five environments. Among them, qCaC.22GY-A05-1 was considered the major QTL, with a phenotypic variation of 10.10%. In addition, 228 single nucleotide polymorphisms significantly related to calcium content were identified using the genome-wide association study in six environments, and they were distributed on all of the chromosomes, except A10. Finally, 10 candidate genes involved in regulating calcium absorption and transport in B. napus shoots were identified. However, no overlapping intervals were found through a comprehensive analysis of the two datasets. These results provide valuable information for understanding the genetic control of calcium concentration in B. napus shoots.

Genetic and transcriptome analyses of the effect of genotype-by-environment interactions on Brassica napus seed oil content

The molecular basis underlying crop traits is complex, with gene-by-environment interactions (GEIs) affecting phenotypes. However, quantitative trait nucleotide (QTN)-by-environment interactions (QEIs) and GEIs for seed oil content (SOC) in oil crops are rare. Here, we detected 11 environmentally specific and 10 stable additive QTNs and 11 QEIs for SOC in rapeseed (Brassica napus) using genome-wide association studies. Weighted gene co-expression network analysis identified 8 Environmental-Developmental Gene co-expression Modules for which the eigengenes correlated with SOC and the environment explained a large proportion of the variance in gene expression. By incorporating information from the multi-omics dataset, 17 candidate genes and 11 candidate GEIs for SOC were predicted. We mined 1 GEI candidate, LIGHT-DEPENDENT SHORT HYPOCOTYLS5 (LSH5), around the environmentally specific QTN qspOC.A02.1 and QEI qeOC.A02.1 detected by climatic indices as covariates. BnaA02.LSH5 was highly expressed in early seed development, and its expression varied significantly across planting sites, with a trend opposite to light-related climatic indices. The BnaA02.lsh5 and BnaC02.lsh5 double mutants had lower SOC, hypocotyl length, photosynthesis, and carbon- and energy-related metabolites compared with wild type. Moreover, BnaA02.LSH5 transcriptionally directly repressed BnaA02.pMDH2 in fatty acid β-oxidation and photosynthetic electron transport. We propose that BnaLSH5 affects seed oil accumulation in response to light intensity. This study provides a basis for creating high-oil germplasm that is adapted to specific environments.

Comparative transcriptome analysis identified candidate genes associated with kernel row number in maize

Kernel row number (KRN) is a crucial trait in maize that has a high impact on yield. However, KRN is a typical quantitative trait with only a few genes being verified so far. Here, two maize inbred lines with contrasting KRN were used to perform transcriptome analysis at five early ear developmental stages. Pairwise differential gene expression analyses were performed, and a total of 11,897 line-specific differentially expressed genes (DEGs) were detected between the two lines across the five development stages. Clustering analysis of line-specific DEGs revealed that the trends of gene expression changed significantly in the five stages, thus the five stages were further divided into two development phases: Phase I (V6-V8) and Phase II (V9-V10). Gene ontology enrichment analysis revealed that different transcriptional pathways were activated in the two phases. DEGs in Phase I were significantly enriched in morphogenesis and differentiation processes and hormone regulation. Of the 5,850 line-specific DEGs in Phase I, 2,132 genes were in known quantitative trait loci (QTLs) or flanking regions of quantitative trait nucleotides (QTNs), of which 92 were repeatedly detected in QTLs where QTNs also exist. The 92 high-probability candidate genes included development-related transcription factors (SBP-box and AP2/EREBP TFs) as well as genes involved in hormone homeostasis and signaling. Our study provides genetic resources for the elucidation of the molecular mechanisms of KRN development and reference for the cloning of candidate genes.

Identification of SNP markers associated with yield in winter oilseed rape (Brassica napus L.) hybrids

Winter oilseed rape (Brassica napus), a crucial crop in temperate regions, is a key contributor to global vegetable oil production and an essential component of crop rotations due to its ability to improve soil structure and fertility. Enhancing its yield is vital for meeting the increasing demand for sustainable oil production, supporting food security, and optimizing biofuel production, while also ensuring the economic viability of agricultural systems in colder climates. The aim of the research was to determine association between SNP molecular markers and rapeseed yield. The plant material for this study consisted of 276 oilseed rape hybrids. The experiment was conducted in four localities: Borowo, Kończewice, Małyszyn, and Strzelce. The mean yield values ranged from 0.07 kg (for hybrid EH_20212 in Małyszyn) to 9.10 kg (for hybrid EH_20410 in Kończewice). The genotype matrix for 276 hybrids was constructed using marker data from the parental genotypes of inbred individuals (maternal and paternal lines). The matrix was coded as {- 1, 0, 1}, assuming an additive effect of the alleles. A total of 13,116 SNP markers were identified. For association mapping, 12,581 polymorphic markers were used. The results of the observation of the yield and sequencing were used for association mapping, which ultimately resulted in the selection of twenty-six molecular markers important (LOD > 5.0) simultaneously in all four localities.

Breeding and biotechnology approaches to enhance the nutritional quality of rapeseed byproducts for sustainable alternative protein sources- a critical review

Global protein consumption is increasing exponentially, which requires efficient identification of potential, healthy, and simple protein sources to fulfil the demands. The existing sources of animal proteins are high in fat and low in fiber composition, which might cause serious health risks when consumed regularly. Moreover, protein production from animal sources can negatively affect the environment, as it often requires more energy and natural resources and contributes to greenhouse gas emissions. Thus, finding alternative plant-based protein sources becomes indispensable. Rapeseed is an important oilseed crop and the world's third leading oil source. Rapeseed byproducts, such as seed cakes or meals, are considered the best alternative protein source after soybean owing to their promising protein profile (30%-60% crude protein) to supplement dietary requirements. After oil extraction, these rapeseed byproducts can be utilized as food for human consumption and animal feed. However, anti-nutritional factors (ANFs) like glucosinolates, phytic acid, tannins, and sinapines make them unsuitable for direct consumption. Techniques like microbial fermentation, advanced breeding, and genome editing can improve protein quality, reduce ANFs in rapeseed byproducts, and facilitate their usage in the food and feed industry. This review summarizes these approaches and offers the best bio-nutrition breakthroughs to develop nutrient-rich rapeseed byproducts as plant-based protein sources.

Integrating GWAS, RNA-Seq and functional analysis revealed that BnaA02.SE mediates silique elongation by affecting cell proliferation and expansion in Brassica napus

Rapeseed (Brassica napus) silique is the major carbohydrate source for seed development, and the final silique length has attracted great attention from breeders. However, no studies had focused on the dynamic character of silique elongation length (SEL). Here, the dynamic SEL investigation in a natural population including 588 lines over two years indicate that dynamic SEL during 0-20 days after flowering was the most essential stage associated with seed number per silique (SPS) and thousand seed weight (TSW). Then, nine loci were identified to be associated with SEL based on GWAS analysis, among which five SNPs (over 50%) distributed on the A02 chromosome within 6.08 to 6.48 Mb. Subsequently, we screened 5078 differentially expressed genes between two extreme materials. An unknown protein, BnaA02.SE, was identified combining with GWAS and RNA-Seq analysis. Subcellular localization and expression profiles analysis demonstrated that BnaA02.SE is a chloroplast- and nucleus-localized protein mainly expressed in pericarps and leaves. Furthermore, transgenic verification and dynamic cytological observation reveal that overexpressed BnaA02.SE can promote silique elongation by regulating JA and IAA contents, affecting cell proliferation and expansion, respectively, and finally enhance seed yield by influencing SPS and TSW. Haplotype analysis reveal that the homologs of BnaA02.SE may also be involved in silique elongation regulation. Our findings provided comprehensive insights into a newly SEL trait, and cloned the first gene (BnaA02.SE) controlling silique elongation in B. napus. The identified BnaA02.SE and its homologs can offer a valuable target for improving B. napus yield.

Functional genomics of Brassica napus: Progresses, challenges, and perspectives

Brassica napus, commonly known as rapeseed or canola, is a major oil crop contributing over 13% to the stable supply of edible vegetable oil worldwide. Identification and understanding the gene functions in the B. napus genome is crucial for genomic breeding. A group of genes controlling agronomic traits have been successfully cloned through functional genomics studies in B. napus. In this review, we present an overview of the progress made in the functional genomics of B. napus, including the availability of germplasm resources, omics databases and cloned functional genes. Based on the current progress, we also highlight the main challenges and perspectives in this field. The advances in the functional genomics of B. napus contribute to a better understanding of the genetic basis underlying the complex agronomic traits in B. napus and will expedite the breeding of high quality, high resistance and high yield in B. napus varieties.

Fine mapping and candidate gene analysis of a major QTL for oil content in the seed of Brassica napus

KEY MESSAGE

By integrating QTL fine mapping and transcriptomics, a candidate gene responsible for oil content in rapeseed was identified. The gene is anticipated to primarily function in photosynthesis and photosystem metabolism pathways. Brassica napus is one of the most important oil crops in the world, and enhancing seed oil content is an important goal in its genetic improvement. However, the underlying genetic basis for the important trait remains poorly understood in this crop. We previously identified a major locus, OILA5 responsible for seed oil content on chromosome A5 through genome-wide association study. To better understand the genetics of the QTL, we performed fine mapping of OILA5 with a double haploid population and a BC3F2 segregation population consisting of 6227 individuals. We narrowed down the QTL to an approximate 43 kb region with twelve annotated genes, flanked by markers ZDM389 and ZDM337. To unveil the potential candidate gene responsible for OILA5, we integrated fine mapping data with transcriptome profiling using high and low oil content near-isogenic lines. Among the candidate genes, BnaA05G0439400ZS was identified with high expression levels in both seed and silique tissues. This gene exhibited homology with AT3G09840 in Arabidopsis that was annotated as cell division cycle 48. We designed a site-specific marker based on resequencing data and confirmed its effectiveness in both natural and segregating populations. Our comprehensive results provide valuable genetic information not only enhancing our understanding of the genetic control of seed oil content but also novel germplasm for advancing high seed oil content breeding in B. napus and other oil crops.

Transcriptomic Profiling of Shoot Apical Meristem Aberrations in the Multi-Main-Stem Mutant (ms) of Brassica napus L

Rapeseed (Brassica napus L.) is a globally important oilseed crop with various uses, including the consumption of its succulent stems as a seasonal vegetable, but its uniaxial branching habit limits the stem yield. Therefore, developing a multi-stem rapeseed variety has become increasingly crucial. In this study, a natural mutant of the wild type (ZY511, Zhongyou511) with stable inheritance of the multi-stem trait (ms) was obtained, and it showed abnormal shoot apical meristem (SAM) development and an increased main stem number compared to the WT. Histological and scanning electron microscopy analyses revealed multiple SAMs in the ms mutant, whereas only a single SAM was found in the WT. Transcriptome analyses showed significant alterations in the expression of genes involved in cytokinin (CK) biosynthesis and metabolism pathways in the ms mutant. These findings provide insight into the mechanism of multi-main-stem formation in Brassica napus L. and lay a theoretical foundation for breeding multi-main-stem rapeseed vegetable varieties.

Factors Affecting the Quality of Canola Grains and Their Implications for Grain-Based Foods

Canola, Brassica napus L., is a major oilseed crop that has various uses in the food, feed, and industrial sectors. It is one of the most widely produced and consumed oilseeds in the world because of its high oil content and favorable fatty acid composition. Canola grains and their derived products, such as canola oil, meal, flour, and bakery products, have a high potential for food applications as they offer various nutritional and functional benefits. However, they are affected by various factors during the production cycle, post-harvest processing, and storage. These factors may compromise their quality and quantity by affecting their chemical composition, physical properties, functional characteristics, and sensory attributes. Therefore, it is important to optimize the production and processing methods of canola grains and their derived products to ensure their safety, stability, and suitability for different food applications. This literature review provides a comprehensive overview of how these factors affect the quality of canola grains and their derived products. The review also suggests future research needs and challenges for enhancing canola quality and its utilization in food.

Integrating GWAS, linkage mapping and gene expression analyses reveal the genetic control of first branch height in Brassica napus L

Rapeseed (Brassica napus L.) is a crucial oil crop cultivated worldwide. First branch height, an essential component of rapeseed plant architecture, has an important effect on yield and mechanized harvesting; however, the underlying genetic mechanism remains unclear. In this study, based on the 60K single nucleotide polymorphism array and a recombinant inbred lines population derived from M083 and 888-5, a total of 19 QTLs were detected in five environments, distributed on linkage groups A02, A09, A10, C06, and C07, which explained phenotypic variation ranging from 4.87 to 29.87%. Furthermore, 26 significant SNPs were discovered on Chr.A02 by genome-wide association study in a diversity panel of 324 re-sequencing accessions. The major QTL of the first branch height trait was co-located on Chr.A02 by integrating linkage mapping and association mapping. Eleven candidate genes were screened via allelic variation analysis, inter-subgenomic synteny analysis, and differential expression of genes in parental shoot apical meristem tissues. Among these genes, BnaA02g13010D, which encodes a TCP transcription factor, was confirmed as the target gene according to gene function annotation, haplotype analysis, and full-length gene sequencing, which revealed that TATA insertion/deletion in the promoter region was closely linked to significantly phenotypic differences BnaA02.TCP1 ^M083 overexpression resulted in decreased branch height and increased branch number in Arabidopsis. These results provide a genetic basis for first branch height and the ideal architecture of B. napus.

Genome-Wide Association Studies of Salt Tolerance at the Seed Germination Stage and Yield-Related Traits in Brassica napus L

Salt stress severely affects crop growth and development and reduces the yield of Brassica napus. Exploring natural genetic variations for high salt tolerance in B. napus seedlings is an effective approach to improve productivity under salt stress. Using 10,658 high-quality single nucleotide polymorphic (SNP) markers developed by specific-locus amplified fragment sequencing (SLAF-seq) technology, genome-wide association studies (GWAS) were performed to investigate the genetic basis of salt tolerance and yield-related traits of B. napus. The results revealed that 77 and 497 SNPs were significantly associated with salt tolerance and yield-related traits, of which 40 and 58 SNPs were located in previously reported QTLs/SNPs, respectively. We identified nineteen candidate genes orthologous with Arabidopsis genes known to be associated with salt tolerance and seven potential candidates controlling both salt tolerance and yield. Our study provides a novel genetic resource for the breeding of high-yield cultivars resistant to salt stress.

Genome-wide association study reveals a GLYCOGEN SYNTHASE KINASE 3 gene regulating plant height in Brassica napus

Rapeseed (Brassica napus) is an allotetraploid crop that is the main source of edible oils and feed proteins in the world. The ideal plant architecture breeding is a major objective of rapeseed breeding and determining the appropriate plant height is a key element of the ideal plant architecture. Therefore, this study aims to improve the understanding of the genetic controls underlying plant height. The plant heights of 230 rapeseed accessions collected worldwide were investigated in field experiments over two consecutive years in Wuhan, China. Whole-genome resequencing of these accessions yielded a total of 1,707,194 informative single nucleotide polymorphisms (SNPs) that were used for genome-wide association analysis (GWAS). GWAS and haplotype analysis showed that BnaA01g09530D, which encodes BRASSINOSTEROID-INSENSITIVE 2 and belongs to the GLYCOGEN SYNTHASE KINASE 3 (GSK3) family, was significantly associated with plant height in B. napus. Moreover, a total of 31 BnGSK3s with complete domains were identified from B. napus genome and clustered into four groups according to phylogenetic analysis, gene structure, and motif distribution. The expression patterns showed that BnGSK3s exhibited significant differences in 13 developmental tissues in B. napus, suggesting that BnGSK3s may be involved in tissue-specific development. Sixteen BnGSK3 genes were highly expressed the in shoot apical meristem, which may be related to plant height or architecture development. These results are important for providing new haplotypes of plant height in B. napus and for extending valuable genetic information for rapeseed genetic improvement of plant architecture.

Genome-wide identification and comparative analysis of CLE family in rapeseed and its diploid progenitors

Crop genomics and breeding CLAVATA3/EMBRYO SURROUNDING REGION-RELATED (CLE) proteins belong to a small peptide family in plants. During plant development, CLE gene family members play a pivotal role in regulating cell-to-cell communication and stem cell maintenance. However, the evolutionary process and functional importance of CLEs are unclear in Brassicaceae. In this study, a total of 70 BnCLEs were identified in Brassica napus (2n = 4x = 38, A_nC_n): 32 from the A_n subgenome, 36 from the C_n subgenome, and 2 from the unanchored subgenome. Meanwhile, 29 BrCLE and 32 BoCLE genes were explored in Brassica rapa (2n = 2x = 20, A_r) and Brassica oleracea (2n = 2x = 18, C_o). Phylogenetic analysis revealed that 163 CLEs derived from three Brassica species and Arabidopsis thaliana can be divided into seven subfamilies. Homology and synteny analyses indicated whole-genome triplication (WGT) and segmental duplication may be the major contributors to the expansion of CLE family. In addition, RNA-seq and qPCR analysis indicated that 19 and 16 BnCLEs were more highly expressed in immature seeds and roots than in other tissues. Some CLE gene pairs exhibited different expression patterns in the same tissue, which indicated possible functional divergence. Furthermore, genetic variations and regional association mapping analysis indicated that 12 BnCLEs were potential genes for regulating important agronomic traits. This study provided valuable information to understand the molecular evolution and biological function of CLEs in B. napus and its diploid progenitors, which will be helpful for genetic improvement of high-yield breeding in B. napus.