“…In such an allohexaploid, it would also be possible to take advantage of “fixed heterosis” (Abel et al 2005 ), where the heterosis is present between the subgenomes (A, B, and C) can be maintained in inbreeding lines. In addition, new phenotypes which are not present in the original parents may develop from the different crosses via novel mutations due to the hybridization event (Udall and Wendel 2006 ; Kaur et al 2014 ). Fig.…”
In the Brassica genus, we find both diploid species (one genome) and allotetraploid species (two different genomes) but no naturally occurring hexaploid species (three different genomes, AABBCC). Although hexaploids can be produced via human intervention, these neo-polyploids have quite unstable genomes and usually suffer from severe genome reshuffling. Whether these genome rearrangements continue in later generations and whether genomic arrangements follow similar, reproducible patterns between different lineages is still unknown. We crossed Brassica hexaploids resulting from different species combinations to produce five F1 hybrids and analyzed the karyotypes of the parents and the F1 hybrids, as well as allele segregation in a resulting test-cross population via molecular karyotyping using SNP array genotyping. Although some genomic regions were found to be more likely to be duplicated, deleted, or rearranged, a consensus pattern was not shared between genotypes. Brassica hexaploids had a high tolerance for fixed structural rearrangements, but which rearrangements occur and become fixed over many generations does not seem to show either strong reproducibility or to indicate selection for stability. On average, we observed 10 de novo chromosome rearrangements contributed almost equally from both parents to the F1 hybrids. At the same time, the F1 hybrid meiosis produced on average 8.6 new rearrangements. Hence, the increased heterozygosity in the F1 hybrid did not significantly improve genome stability in our hexaploid hybrids and might have had the opposite effect. However, hybridization between lineages was readily achieved and may be exploited for future genetics and breeding purposes.
“…In such an allohexaploid, it would also be possible to take advantage of “fixed heterosis” (Abel et al 2005 ), where the heterosis is present between the subgenomes (A, B, and C) can be maintained in inbreeding lines. In addition, new phenotypes which are not present in the original parents may develop from the different crosses via novel mutations due to the hybridization event (Udall and Wendel 2006 ; Kaur et al 2014 ). Fig.…”
In the Brassica genus, we find both diploid species (one genome) and allotetraploid species (two different genomes) but no naturally occurring hexaploid species (three different genomes, AABBCC). Although hexaploids can be produced via human intervention, these neo-polyploids have quite unstable genomes and usually suffer from severe genome reshuffling. Whether these genome rearrangements continue in later generations and whether genomic arrangements follow similar, reproducible patterns between different lineages is still unknown. We crossed Brassica hexaploids resulting from different species combinations to produce five F1 hybrids and analyzed the karyotypes of the parents and the F1 hybrids, as well as allele segregation in a resulting test-cross population via molecular karyotyping using SNP array genotyping. Although some genomic regions were found to be more likely to be duplicated, deleted, or rearranged, a consensus pattern was not shared between genotypes. Brassica hexaploids had a high tolerance for fixed structural rearrangements, but which rearrangements occur and become fixed over many generations does not seem to show either strong reproducibility or to indicate selection for stability. On average, we observed 10 de novo chromosome rearrangements contributed almost equally from both parents to the F1 hybrids. At the same time, the F1 hybrid meiosis produced on average 8.6 new rearrangements. Hence, the increased heterozygosity in the F1 hybrid did not significantly improve genome stability in our hexaploid hybrids and might have had the opposite effect. However, hybridization between lineages was readily achieved and may be exploited for future genetics and breeding purposes.
“…Organellar genomes have long been used as materials to address evolutionary questions regarding Brassica taxa, especially the three allotetraploid species. Previous studies using cp and mt genomic data overwhelmingly support the hypothesis that the maternal source of B. juncea comes from B. rapa (Li et al, 2017;Kim et al, 2018) but two studies based on a large number of B. juncea varieties, discovered multiple origins of the allotetraploid (Chen et al, 2013) and a few varieties with a maternal origin of B. nigra (Kaur et al, 2014). In fact, B. nigra has been suggested to be the maternal parent of another allotetraploid B. carinata (Yamagishi et al, 2014;Yang et al, 2016b;Li et al, 2017) but it's not known if there is an undiscovered B. carinata variety with a maternal parent of B. oleracea.…”
The sequences and genomic structures of plant mitochondrial (mt) genomes provide unique material for phylogenetic studies. The nature of uniparental inheritance renders an advantage when utilizing mt genomes for determining the parental sources of hybridized taxa. In this study, a concatenated matrix of mt genes was used to infer the phylogenetic relationships of six cultivated Brassica taxa and explore the maternal origins of three allotetraploids. The well-resolved sister relationships between two pairs of diploid and allotetraploid taxa suggest that Brassica carinata (car) possessed a maternal origin from Brassica nigra, while Brassica juncea (jun) was maternally derived from Brassica rapa (cam). Another allotetraploid taxon, Brassica napus (cv. Wester) may have been maternally derived from the common ancestor of B. rapa and Brassica oleracea (ole), and/or have undergone (an) extra hybridization event(s) along its evolutionary history. The characteristics of Brassica mt genomic structures also supported the phylogenetic results. Sinapis arvensis was nested inside the Brassica species, sister to the B. nigra-B. carinata lineage, and possessed an mt genome structure that mostly resembled B. nigra. Collectively, the evidence supported a systematic revision that placed S. arvensis within Brassica. Finally, ancestral mt genomes at each evolutionary node of Brassica were reconstructed, and the detailed and dynamic evolution of Brassica mt genomes was successfully reproduced. The mt genome of B. nigra structurally resembled that of the Brassica ancestor the most, with only one reversion of a block, and the Brassica oleracea underwent the most drastic changes. These findings suggested that repeat-mediated recombinations were largely responsible for the observed structural variations in the evolutionary history of Brassica mt genomes.
“…Plant growth habits (in particular, indeterminate or determinate inflorescences) have an important effect on the architecture and yield of plants such as oilseed [3,6,32], soybean [33,34], and tomato [35]. The development of the SAM determines the plant growth habit; the SAM is located at the top of the stem of the plant and is mainly composed of cells with unlimited growth capacity [36][37][38].…”
Determinate inflorescences have a significant effect on the genetic improvement of rapeseed, so understanding the molecular function underlying the inflorescence trait may be beneficial to oilseed breeding. A previous study found candidate gene BnTFL1 (Terminal Flower 1) for control of the inflorescence trait on Brassica napus chromosome A10 (16,627–16,847 kb). However, little is known about the function of the BnTFL1 gene in B. napus. In this study, we firstly studied the formation of the shoot apical meristem and gene expression in indeterminate and determinate inflorescences; the results showed that the inflorescence architecture and BnA10.TFL1 expression showed significant differences in the shoot apex at the budding stage. Then, two alleles (named BnA10.TFL1 gene from indeterminate and BnA10.tfl1 gene from determinate) were cloned and sequence-analyzed; the results suggest that the open reading frame of the alleles comprises 537 bp, encodes 178 amino acids containing a conserved phosphatidylethanolamine-binding protein (PEBP) domain, and shares high similarity with Arabidopsis thaliana TFL1. To analyze the function of BnA10.TFL1, the BnA10.TFL1 gene was introduced into the determinate A. thaliana tfl1 mutant and B. napus 571 line by complementation experiment. The determinate traits were restored to indeterminate, and expression of BnA10.TFL1 was increased in the indeterminate shoot apex. These results reveal that BnA10.tfl1 is a gene controlling the determinate inflorescence trait. Moreover, the BnA10.TFL1 protein was localized to the nucleus, cytoplasm, and plasma membrane. Collectively, the results of this study help us to understand the molecular mechanism of determinate inflorescences and will provide a reliable research basis for the application of determinate inflorescences in B. napus.
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