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Quezada Martinez, D.

Publications and source records attributed to Quezada Martinez, D..

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bioRxiv2023

Karyotype instability varies by species and genotype combination in allohexaploid Brassica

Synthetic Brassica allohexaploids (2n = AABBCC) do not exist naturally but can be produced between six different parent species combinations, and can be used to investigate processes of polyploid formation and genome stabilization. In this study, we investigated hybridization potential, accumulation and frequency of copy number variants (CNVs), fertility, and karyotype stability in advanced generations of diverse allohexaploid genotypes belonging to different Brassica allohexaploid species combinations (NCJ types: B. napus x B. carinata x B. juncea; junleracea types: B. juncea x B. oleracea; naponigra types: B. napus x B. nigra; and carirapa types: B. rapa x B. carinata). Only 3.2% of allohexaploid plants investigated were euploids, with high frequencies of rearrangements. Significant differences between genotypes and between lineages within parent genotype combinations were found for frequencies of euploids and rearrangements, with one NCJ line showing relatively high karyotype stability. Hybridization between different allohexaploids was mostly achievable, with 0 - 4.6 seeds per flower bud on average, and with strong effects of maternal genotype. Novel hybrids between allohexaploid lineages showed similar fertility and stability to their parents. In the novel hybrid population, a significant correlation was observed between the inheritance of A-genome chromosome fragments (relative to C-genome fragments) and the total number of seeds produced per plant (r = 0.24). Our results suggest that synthetic Brassica allohexaploids can develop genomic stability, but that this occurs at very low frequencies, and may not always be under selective pressure due to the unpredictable relationship between fertility and genome composition in these hybrid types. Article SummaryBrassica plants with three sets of chromosomes (allohexaploids) do not exist in nature, but can be made from combinations between six different species. Here, we compared different combinations to see which are the most genomically stable and fertile, and found major differences between all allohexaploid types as well as one putatively stable line. Crosses between allohexaploid types could also be achieved in most cases, although hybrids were not more stable or fertile than their parents.

genetics↗
bioRxiv2021

Allele segregation analysis of F1 hybrids between independent Brassica allohexaploid lineages

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 lines 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.

genetics↗