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Exploring the gene pool of Brassica napus by genomics-based approaches.

ABSTRACT: De novo allopolyploidization in Brassica provides a very successful model for reconstructing polyploid genomes using progenitor species and relatives to broaden crop gene pools and understand genome evolution after polyploidy, interspecific hybridization and exotic introgression. B. napus (AACC), the major cultivated rapeseed species and the third largest oilseed crop in the world, is a young Brassica species with a limited genetic base resulting from its short history of domestication, cultivation, and intensive selection during breeding for target economic traits. However, the gene pool of B. napus has been significantly enriched in recent decades that has been benefit from worldwide effects by the successful introduction of abundant subgenomic variation and novel genomic variation via intraspecific, interspecific and intergeneric crosses. An important question in this respect is how to utilize such variation to breed crops adapted to the changing global climate. Here, we review the genetic diversity, genome structure, and population-level differentiation of the B. napus gene pool in relation to known exotic introgressions from various species of the Brassicaceae, especially those elucidated by recent genome-sequencing projects. We also summarize progress in gene cloning, trait-marker associations, gene editing, molecular marker-assisted selection and genome-wide prediction, and describe the challenges and opportunities of these techniques as molecular platforms to exploit novel genomic variation and their value in the rapeseed gene pool. Future progress will accelerate the creation and manipulation of genetic diversity with genomic-based improvement, as well as provide novel insights into the neo-domestication of polyploid crops with novel genetic diversity from reconstructed genomes.

SUBMITTER: Hu D

PROVIDER: S-EPMC8428838 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Use of host resistance is the most economical and environmentally safe way to control light leaf spot disease of oilseed rape (Brassica napus). The causal organism of light leaf spot, Pyrenopeziza brassicae, is one of the most economically damaging pathogens of oilseed rape in the United Kingdom and it is considered to have a high potential to evolve due to its mixed reproduction system and airborne ascospores. This necessitates diverse sources of host resistance, which are inadequate at present to minimize yield losses caused by this disease. To address this, we screened a doubled haploid (DH) population of oilseed rape, derived from a secondary gene pool (ancestral genomes) of B. napus for the introgression of resistance against P. brassicae. DH lines were phenotyped using controlled-environment and glasshouse experiments with P. brassicae populations obtained from three different geographic locations in the United Kingdom. Selected DH lines with different levels of resistance were further studied in a controlled-environment experiment using both visual (scanning electron microscope - SEM) and molecular (quantitative PCR) assessment methods to understand the mode/s of host resistance. There was a clear phenotypic variation for resistance against P. brassicae in this DH population. Quantitative trait locus (QTL) analysis identified four QTLs with moderate to large effects, which were located on linkage groups C1, C6, and C9. Of these, the QTL on the linkage group C1 appeared to have a major effect on limiting P. brassicae asexual sporulation. Study of the sub-cuticular growth phase of P. brassicae using qPCR and SEM showed that the pathogen was able to infect and colonise both resistant and susceptible Q DH lines and control B. napus cultivars. However, the rate of increase of pathogen biomass was significantly smaller in resistant lines, suggesting that the resistance segregating in this DH population limits colonisation/sporulation by the pathogen rather than eliminating the pathogen. Resistance QTLs identified in this study provide a useful resource for breeding cultivar resistance for effective control of light leaf spot and form a starting point for functional identification of the genes controlling resistance against P. brassicae that can contribute to our knowledge on mechanisms of partial resistance of crops against pathogens.

Project description:BACKGROUND:The basic helix-loop-helix (bHLH) is the second largest gene family in the plant, some members play important roles in pistil development and response to drought, waterlogging, cold stress and salt stress. The bHLH gene family has been identified in many species, except for Brassica oleracea and B. napus thus far. This study aims to identify the bHLH family members in B. oleracea, B. rapa and B. napus, and elucidate the expression, duplication, phylogeny and evolution characters of them. RESULT:A total of 268 bHLH genes in B. oleracea, 440 genes in B. napus, and 251 genes in B. rapa, including 21 new bHLH members, have been identified. Subsequently, the analyses of the phylogenetic trees, conserved motifs and gene structures showed that the members in the same subfamily were highly conserved. Most Ka/Ks values of homologous gene were?<?1, which indicated that these genes suffered from strong purifying selection for retention. The retention rates of BrabHLH and BolbHLH genes were 51.6 and 55.1%, respectively. The comparative expression patterns between B. rapa and B. napus showed that they had similar expression patterns in the root and contrasting patterns in the stems, leaves, and reproductive tissues. In addition, there were 41 and 30 differential expression bHLH genes under the treatments of ABA and JA, respectively, and the number of down regulation genes was significantly more than up regulation genes. CONCLUSION:In the present study, we identified and performed the comparative genomics analysis of bHLH gene family among B. oleracea, B. rapa and B. napus, and also investigated their diversity. The expression patterns between B. rapa and B. napus shows that they have the similar expression pattern in the root and opposite patterns in the stems, leaves, and reproduction tissues. Further analysis demonstrated that some bHLH gene members may play crucial roles under the abiotic and biotic stress conditions. This is the first to report on the bHLH gene family analysis in B. oleracea and B. napus, which can offer useful information on the functional analysis of the bHLH gene in plants.

Project description:Rapeseed (Brassica napus L.) is the most important oil crop of temperate climates. Rapeseed oil contains tocopherols, also known as vitamin E, which is an indispensable nutrient for humans and animals due to its antioxidant and radical scavenging abilities. Moreover, tocopherols are also important for the oxidative stability of vegetable oils. Therefore, seed oil with increased tocopherol content or altered tocopherol composition is a target for breeding. We investigated the role of nucleotide variations within candidate genes from the tocopherol biosynthesis pathway. Field trials were carried out with 229 accessions from a worldwide B. napus collection which was divided into two panels of 96 and 133 accessions. Seed tocopherol content and composition were measured by HPLC. High heritabilities were found for both traits, ranging from 0.62 to 0.94. We identified polymorphisms by sequencing selected regions of the tocopherol genes from the 96 accession panel. Subsequently, we determined the population structure (Q) and relative kinship (K) as detected by genotyping with genome-wide distributed SSR markers. Association studies were performed using two models, the structure-based GLM + Q and the PK-mixed model. Between 26 and 12 polymorphisms within two genes (BnaX.VTE3.a, BnaA.PDS1.c) were significantly associated with tocopherol traits. The SNPs explained up to 16.93% of the genetic variance for tocopherol composition and up to 10.48% for total tocopherol content. Based on the sequence information we designed CAPS markers for genotyping the 133 accessions from the second panel. Significant associations with various tocopherol traits confirmed the results from the first experiment. We demonstrate that the polymorphisms within the tocopherol genes clearly impact tocopherol content and composition in B. napus seeds. We suggest that these nucleotide variations may be used as selectable markers for breeding rapeseed with enhanced tocopherol quality.

Project description:Auxin response factor (ARF) is a member of the plant-specific B3 DNA binding superfamily. Here, we report the results of a comprehensive analysis of ARF genes in allotetraploid Brassica napus (2n = 38, AACC). Sixty-seven ARF genes were identified in B. napus (BnARFs) and divided into four subfamilies (I-IV). Sixty-one BnARFs were distributed on all chromosomes except C02; the remaining were on Ann and Cnn. The full length of the BnARF proteins was highly conserved especially within each subfamily with all members sharing the N-terminal DNA binding domain (DBD) and the middle region (MR), and most contained the C-terminal dimerization domain (PBI). Twenty-one members had a glutamine-rich MR that may be an activator and the remaining were repressors. Accordingly, the intron patterns are highly conserved in each subfamily or clade, especially in DBD and PBI domains. Several members in subfamily III are potential targets for miR167. Many putative cis-elements involved in phytohormones, light signaling responses, and biotic and abiotic stress were identified in BnARF promoters, implying their possible roles. Most ARF proteins are likely to interact with auxin/indole-3-acetic acid (Aux/IAA) -related proteins, and members from different subfamilies generally shared many common interaction proteins. Whole genome-wide duplication (WGD) by hybridization between Brassica rapa and Brassica oleracea and segmental duplication led to gene expansion. Gene loss following WGD is biased with the An-subgenome retaining more ancestral genes than the Cn-subgenome. BnARFs have wide expression profiles across vegetative and reproductive organs during different developmental stages. No obvious expression bias was observed between An- and Cn-subgenomes. Most synteny-pair genes had similar expression patterns, indicating their functional redundancy. BnARFs were sensitive to exogenous IAA and 6-BA treatments especially subfamily III. The present study provides insights into the distribution, phylogeny, and evolution of ARF gene family.

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Exploring the gene pool of Brassica napus by genomics-based approaches.

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