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New Phytol. 2019 Jul;223(2):965-978. doi: 10.1111/nph.15804. Epub 2019 Apr 24.

Inherited allelic variants and novel karyotype changes influence fertility and genome stability in Brassica allohexaploids.

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Department of Plant Breeding, Justus Liebig University, Heinrich-Buff-Ring 26-32, Giessen, 35392, Germany.
Faculty of Health Science, Technische Hochschule Mittelhessen, Wiesenstrasse 14, Giessen, 35390, Germany.
School of Biological Sciences and Institute of Agriculture, University of Western Australia, 35 Stirling Hwy, Perth, WA, 6009, Australia.


Synthetic allohexaploid Brassica hybrids (2n = AABBCC) do not exist naturally, but can be synthesized by crosses between diploid and/or allotetraploid Brassica species. Using these hybrids, we aimed to identify how novel allohexaploids restore fertility and normal meiosis after formation. Chromosome inheritance, genome structure, fertility and meiotic behaviour were assessed in three segregating allohexaploid populations derived from the cross (B. napus × B. carinata) × B. juncea using a combination of molecular marker genotyping, phenotyping and cytogenetics. Plants with unbalanced A-C translocations in one direction (where a C-genome chromosome fragment replaces an A-genome fragment) but not the other (where an A-genome fragment replaces a C-genome fragment) showed significantly reduced fertility across all populations. Genomic regions associated with fertility contained several meiosis genes with putatively causal mutations inherited from the parents (copies of SCC2 in the A genome, PAIR1/PRD3, PRD1 and ATK1/KATA/KIN14a in the B genome, and MSH2 and SMC1/TITAN8 in the C genome). Reduced seed fertility associated with the loss of chromosome fragments from only one subgenome following homoeologous exchanges could comprise a mechanism for biased genome fractionation in allopolyploids. Pre-existing meiosis gene variants present in allotetraploid parents may help to stabilize meiosis in novel allohexaploids.


Brassica ; allopolyploids; cytogenetics; genome evolution; meiosis genes; subgenome fractionation


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