We report first-time synthesis of a stable Brassica allohexaploid. It may evolve into a new species and also advance our understanding of pairing regulation and genome evolution in complex allopolyploids.
Crop Brassicas include both monogenomic and digenomic species. A trigenomic Brassica (AABBCC) is not known to exist in nature. Past attempts to synthesize a stable allohexaploid were not successful due to aberrant meiosis and very high proportion of aneuploid plants in the selfed progenies. We report the development of a stable allohexaploid Brassica (2n = 54; AABBCC). Genomic in situ hybridization confirmed the complete assemblage of three genomes. Only allohexaploids involving B. rapa cv. R01 (2n = 20; AA) as pollinator with a set of B. carinata (2n = 34; BBCC) were stable. These exhibited a high proportion (0.78–0.94) of pollen mother cells with normal meiosis and an excellent hexaploid ratio (0.80–0.94) in the selfed progenies. Stability of two allohexaploid combinations was demonstrated from H1 to H4 generations at two very diverse locations in India. Graphical genotyping of allohexaploids allowed detection of chromosome fragment exchanges among three genomes. These were much smaller for meiotically stable allohexaploids as compared to unstable ones. The putative hexaploids were morphologically closer to the female donor, B. carinata, for leaf morphology, inflorescence structure and flower shape. The newly formed allohexaploid may also provide unique opportunities to investigate the immediate genetic and genomic consequences of a Brassica allohexaploid with three resident genomes.
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Research was carried out with the financial assistance received from Department of Biotechnology, Government of India for the project “Creating a new Brassica crop species for food and biofuel” under Indo Australia biotechnology fund (AISRF06520). SSB acknowledges salary support from Indian Council of Agricultural Research from the funds vested with ICAR National Professor Chair project “Broadening the genetic base of Indian mustard (Brassica juncea) through alien introgressions and germplasm enhancement”. Authors thank “Plant Gene Resources of Canada, Agriculture and Agri-Food Canada” for providing several germplasm lines used in these studies.
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The authors declare that they have no conflict of interest.
Communicated by H. C. Becker.
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Gupta, M., Atri, C., Agarwal, N. et al. Development and molecular-genetic characterization of a stable Brassica allohexaploid. Theor Appl Genet 129, 2085–2100 (2016). https://doi.org/10.1007/s00122-016-2759-2
- Pollen Mother Cell
- Homoeologous Chromosome
- Selfed Progeny
- Homoeologous Pairing
- Graphical Genotyping