Genetic And Epigenetic Alterations In Brassica Species Induced By Wide Hybridizations

Allopolyploidization with the merger of the genomes from different species has been shown to be associated with genetic and epigenetic changes. But the maintenance of such alterations related to one parental species after the genome is extracted from the allopolyploid remains to be detected. In this study, the genome of Brassica napus L.(2n=38, genomes AACC) was extracted from its intergeneric allohexaploid(2n=62, genomes AACCOO) with another crucifer Orychophragmus violaceus(2n=24, genome OO), by backcrossing and development of alien addition lines. B. napus-type plants identified in the self-pollinated progenies of nine monosomic additions were analyzed by the methods of amplified fragment length polymorphism(AFLP), sequence-specific amplified polymorphism(SSAP), and methylation-sensitive amplified polymorphism(MSAP). They showed modifications to certain extents in genomic components(loss and gain of DNA segments and transposons, introgression of alien DNA segments) and DNA methylation, compared with B. napus donor. The significant differences in the changes between the B. napus types extracted from these additions likely resulted from the different effects of individual alien chromosomes. Particularly, the additions which harbored the O. violaceus chromosome carrying dominant rRNA genes over those of B. napus tended to result in the development of plants which showed fewer changes, suggesting a role of the expression levels of alien rRNA genes in genomic stability. These results provided new cues for the genetic alterations in one parental genome that are maintained even after the genome becomes independent.The formation and evolution of allopolyploid species have been shown to be accompanied with the genetic and epigenetic changes, but the usual lack of exact parents for an allopolyploid with a long history makes it difficult to detect these alterations specific for the component genomes. Herein, the restituted Brassica rapa(2n=20, AA) which was extracted from the allotetraploid B. napus(2n=38, AACC) by intertribal hybridization was studied for genomic composition, transposon activation and DNA methylation change, in comparison with B. napus donor and natural B. rapa, by the analyses of amplified fragment length polymorphism(AFLP), sequence specific amplified polymorphism(SSAP), and methylation sensitive amplified polymorphism(MSAP). Compared with the B. napus donor, the extracted B. rapa showed high rate of AFLP bands lost, as the C genome missed, but the substantial rate of novel bands likely resulted from the response to the repeated hybridization and even the alien introgression during the extraction. For eleven LTR(Copia) retrotransposons, high frequency of lost SSAP bands but low rate of novel bands appeared. Widespread methylation perturbations occurred in the extracted B. rapa, in comparison with the donor and natural B. rapa. These results suggested that certain extents of genetic and epigenetic alterations were associated with the restituted B. rapa-type, which could be attributed to the evolutionary history of B. napus, the hybridization pathway for extraction(intertribal hybridization, aneuploidization), introgression of alien chromosomal segments, and other factors.