Challenges and prospects for a potential allohexaploid Brassica crop
04 Jun 2021-Theoretical and Applied Genetics (Springer Berlin Heidelberg)-Vol. 134, Iss: 9, pp 2711-2726
TL;DR: In this article, the authors outline the major prospects and challenges and propose possible plans to produce a stable, diverse and agronomically viable allohexaploid Brassica crop.
Abstract: The production of a new allohexaploid Brassica crop (2n = AABBCC) is increasingly attracting international interest: a new allohexaploid crop could benefit from several major advantages over the existing Brassica diploid and allotetraploid species, combining genetic diversity and traits from all six crop species with additional allelic heterosis from the extra genome. Although early attempts to produce allohexaploids showed mixed results, recent technological and conceptual advances have provided promising leads to follow. However, there are still major challenges which exist before this new crop type can be realized: (1) incorporation of sufficient genetic diversity to form a basis for breeding and improvement of this potential crop species; (2) restoration of regular meiosis, as most allohexaploids are genetically unstable after formation; and (3) improvement of agronomic traits to the level of “elite” breeding material in the diploid and allotetraploid crop species. In this review, we outline these major prospects and challenges and propose possible plans to produce a stable, diverse and agronomically viable allohexaploid Brassica crop.
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TL;DR: Results are discussed that show that meiotic stability can be achieved through the differentiation of certain alleles of certain genes between ploidies, and growing evidence suggests that the coevolution of multiple interacting genes has contributed to polyploid stabilization.
Abstract: Newly formed polyploids often show extensive meiotic defects, resulting in aneuploid gametes, and thus reduced fertility. However, while many neopolyploids are meiotically unstable, polyploid lineages that survive in nature are generally stable and fertile; thus, those lineages that survive are those that are able to overcome these challenges. Several genes that promote polyploid stabilization are now known in plants, allowing speculation on the evolutionary origin of these meiotic adjustments. Here, I discuss results that show that meiotic stability can be achieved through the differentiation of certain alleles of certain genes between ploidies. These alleles, at least sometimes, seem to arise by novel mutation, while standing variation in either ancestral diploids or related polyploids, from which alleles can introgress, may also contribute. Growing evidence also suggests that the coevolution of multiple interacting genes has contributed to polyploid stabilization, and in allopolyploids, the return of duplicated genes to single copies (genome fractionation) may also play a role in meiotic stabilization. There is also some evidence that epigenetic regulation may be important, which can help explain why some polyploid lineages can partly stabilize quite rapidly.
8 citations
TL;DR: Pangenome analysis can help to identify the genes underlying stress responses in individuals harbouring untapped genomic diversity in crop wild relatives, which can be applied towards breeding climate resilience into existing crops or to re-domesticating crops, combining environmental adaptation traits with crop productivity.
Abstract: During crop domestication and breeding, wild plant species have been shaped into modern high-yield crops and adapted to the main agro-ecological regions. However, climate change will impact crop productivity in these regions, and agriculture needs to adapt to support future food production. On a global scale, crop wild relatives grow in more diverse environments than crop species, and so may host genes that could support the adaptation of crops to new and variable environments. Through identification of individuals with increased climate resilience we may gain a greater understanding of the genomic basis for this resilience and transfer this to crops. Pangenome analysis can help to identify the genes underlying stress responses in individuals harbouring untapped genomic diversity in crop wild relatives. The information gained from the analysis of these pangenomes can then be applied towards breeding climate resilience into existing crops or to re-domesticating crops, combining environmental adaptation traits with crop productivity.
5 citations
TL;DR: In this article , the authors describe the mechanism of establishment of at least four allopolyploid species in Brassicaceae (Arabidopsis suecica , Arabidopsis kamchatica, Capsella bursa-pastoris, and Brassica napus ), in a manner dependent on the prior loss of the self-incompatibility mechanism in one of the ancestors.
Abstract: Abstract Self-incompatibility systems based on self-recognition evolved in hermaphroditic plants to maintain genetic variation of offspring and mitigate inbreeding depression. Despite these benefits in diploid plants, for polyploids who often face a scarcity of mating partners, self-incompatibility can thwart reproduction. In contrast, self- compatibility provides an immediate advantage: a route to reproductive viability. Thus, diploid selfing lineages may facilitate the formation of new allopolyploid species. Here, we describe the mechanism of establishment of at least four allopolyploid species in Brassicaceae ( Arabidopsis suecica , Arabidopsis kamchatica, Capsella bursa-pastoris, and Brassica napus ), in a manner dependent on the prior loss of the self-incompatibility mechanism in one of the ancestors. In each case, the degraded S -locus from one parental lineage was dominant over the functional S -locus of the outcrossing parental lineage. Such dominant loss-of-function mutations promote an immediate transition to selfing in allopolyploids and may facilitate their establishment.
5 citations
TL;DR: This study lays a good foundation for revealing the molecular regulation of genes related to male and female gamete development in Brassica allohexaploids and provides more resourceful genetic information on the reproductive biology of Brassica polyploid breeding.
Abstract: Polyploidy plays a crucial role in plant evolution and speciation. The development of male and female gametes is essential to the reproductive capacity of polyploids, but their gene expression pattern has not been fully explored in newly established polyploids. The present study aimed to reveal a detailed atlas of gene expression for gamete development in newly synthetic Brassica allohexaploids that are not naturally existing species. Comparative transcriptome profiling between developing anthers (staged from meiosis to mature pollen) and ovules (staged from meiosis to mature embryo sac) was performed using RNA-Seq analysis. A total of 8676, 9775 and 4553 upregulated differentially expressed genes (DEGs) were identified for the development of both gametes, for male-only, and for female-only gamete development, respectively, in the synthetic Brassica allohexaploids. By combining gene ontology (GO) biological process analysis and data from the published literature, we identified 37 candidate genes for DNA double-strand break formation, synapsis and the crossover of homologous recombination during male and female meiosis and 51 candidate genes for tapetum development, sporopollenin biosynthesis and pollen wall development in male gamete development. Furthermore, 23 candidate genes for mitotic progression, nuclear positioning and cell specification and development were enriched in female gamete development. This study lays a good foundation for revealing the molecular regulation of genes related to male and female gamete development in Brassica allohexaploids and provides more resourceful genetic information on the reproductive biology of Brassica polyploid breeding.
2 citations
TL;DR: A doubled haploid (DH) population derived from the cross between two artificially synthesized allohexaploid Brassica was created and self-crossed continuously as mentioned in this paper .
Abstract: Allopolyploids play an essential role in plant evolution and confer apparent advantages on crop growth and breeding compared to low ploidy levels. A doubled haploid (DH) population derived from the cross between two artificially synthesized allohexaploid Brassica was created and self-crossed continuously. Morphological and yield-related traits showed considerable variation among different generations, different families and even within the same families. However, the flowering time, pollen viability and seed yield increased gradually during the selfing process. Ploidy level estimation and karyotyping analysis revealed that this population was chimeras with varied chromosome numbers within an identical plant. Chromosome translocations analysis showed that the B genome was more instable compared to the A and C genomes. The A genome was more prone to chromosome recombination than the C genome. Although some genomic regions were more likely to be duplicated, deleted, or rearranged, a consensus pattern was not shared between different progenies. This research deepened our understanding of the genetic variation of artificially synthesized allohexaploid Brassica. In addition, the allohexaploid Brassica can be used as a bridge to transfer some of the valuable traits blocked by reproductive barriers from wild Brassica species to cultivated species such as cold and drought resistance, etc.
1 citations
References
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TL;DR: The tools of genome research may finally unleash the genetic potential of the authors' wild and cultivated germplasm resources for the benefit of society.
Abstract: Nearly a century has been spent collecting and preserving genetic diversity in plants. Germplasm banks-living seed collections that serve as repositories of genetic variation-have been established as a source of genes for improving agricultural crops. Genetic linkage maps have made it possible to study the chromosomal locations of genes for improving yield and other complex traits important to agriculture. The tools of genome research may finally unleash the genetic potential of our wild and cultivated germplasm resources for the benefit of society.
2,214 citations
TL;DR: The advantages and challenges of polyploidy, and its evolutionary potential, are considered.
Abstract: Polyploids — organisms that have multiple sets of chromosomes — are common in certain plant and animal taxa, and can be surprisingly stable. The evidence that has emerged from genome analyses also indicates that many other eukaryotic genomes have a polyploid ancestry, suggesting that both humans and most other eukaryotes have either benefited from or endured polyploidy. Studies of polyploids soon after their formation have revealed genetic and epigenetic interactions between redundant genes. These interactions can be related to the phenotypes and evolutionary fates of polyploids. Here, I consider the advantages and challenges of polyploidy, and its evolutionary potential.
1,882 citations
Civil Aviation Authority of Singapore1, Rothamsted Research2, University of Copenhagen3, Beijing Institute of Genomics4, Rural Development Administration5, John Innes Centre6, North China University of Science and Technology7, University of Georgia8, University of California, Berkeley9, University of Missouri10, University of Queensland11, Australian Research Council12, National Research Council13, Bielefeld University14, Australian Centre for Plant Functional Genomics15, University of Rennes16, Wageningen University and Research Centre17, Agriculture and Agri-Food Canada18, Huazhong Agricultural University19, French Alternative Energies and Atomic Energy Commission20, Chungnam National University21, Norwich Research Park22
TL;DR: The annotation and analysis of the draft genome sequence of Brassica rapa accession Chiifu-401-42, a Chinese cabbage, and used Arabidopsis thaliana as an outgroup for investigating the consequences of genome triplication, such as structural and functional evolution.
Abstract: We report the annotation and analysis of the draft genome sequence of Brassica rapa accession Chiifu-401-42, a Chinese cabbage. We modeled 41,174 protein coding genes in the B. rapa genome, which has undergone genome triplication. We used Arabidopsis thaliana as an outgroup for investigating the consequences of genome triplication, such as structural and functional evolution. The extent of gene loss (fractionation) among triplicated genome segments varies, with one of the three copies consistently retaining a disproportionately large fraction of the genes expected to have been present in its ancestor. Variation in the number of members of gene families present in the genome may contribute to the remarkable morphological plasticity of Brassica species. The B. rapa genome sequence provides an important resource for studying the evolution of polyploid genomes and underpins the genetic improvement of Brassica oil and vegetable crops.
1,811 citations
TL;DR: New technologies must be developed to accelerate breeding through improving genotyping and phenotyping methods and by increasing the available genetic diversity in breeding germplasm.
Abstract: To feed the several billion people living on this planet, the production of high-quality food must increase with reduced inputs, but this accomplishment will be particularly challenging in the face of global environmental change. Plant breeders need to focus on traits with the greatest potential to increase yield. Hence, new technologies must be developed to accelerate breeding through improving genotyping and phenotyping methods and by increasing the available genetic diversity in breeding germplasm. The most gain will come from delivering these technologies in developing countries, but the technologies will have to be economically accessible and readily disseminated. Crop improvement through breeding brings immense value relative to investment and offers an effective approach to improving food security.
1,777 citations