Location: Plant Genetics ResearchTitle: Genomes Behave as Social Entities: Alien Chromatin Minorities Evolve Through Specificities Reduction Author
Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/12/2010
Publication Date: 3/12/2010
Citation: Bento, M., Gustafson, J.P., Viegas, W., Silva, M. 2010. Genomes Behave as Social Entities: Alien Chromatin Minorities Evolve Through Specificities Reduction. Theoretical and Applied Genetics. 121(3):489-497. 10.1007/s00122-010-1325-6. Interpretive Summary: Many evolutionary studies have shown that major differences exist in the amount of DNA present between the hybrid and the parents that produced the hybrid. Generally large amounts of DNA is lost in the hybrid and this DNA loss comes from only one of the parents. A comparison of the DNA changes that take place when two species of grasses (wheat and rye) are combined into a hybrid (triticale) was undertaken in order to characterize the lost DNA and to understand the major differences that occur in a wheat-rye hybrid. The analysis of wheat, rye, the hybrid, and wheat-rye addition lines (when an individual rye chromosome is added to wheat) was conducted using various molecular systems that characterized different types of DNA. The results revealed that a majority of the non-expressed DNA sequences contained in the rye parent were significantly altered and even deleted when placed into a wheat background. The implications of this study clearly showed that the DNA composition of grass genomes can and does change during polyploid formation to create new species.
Technical Abstract: Hybridization and chromosome doubling entailed by allopolyploidization requires genetic and epigenetic modifications, resulting in the adjustment of different genomes to the same nuclear environment. Recently, the main role of retrotransposon/microsatellite-rich regions of the genome in DNA sequence restructuring events in triticale was disclosed (Bento et al 2008). The present work uses Inter-Retrotransposon Amplified Polymorphisms (IRAP) and Retrotransposon Microsatellite Amplified Polymorphisms (REMAP) to assess genetic rearrangements induced in wheat-rye addition lines obtained by the controlled backcross of octoploid triticale to hexaploid wheat. In the comparative analysis of banding profiles comparing the complete set of seven wheat/rye disomic addition lines, the triticale, rye, and wheat parents disclosed an absence of variability between wheat and wheat-rye addition lines patterns for the five different primer combinations used. Rye-origin bands as well as triticale-specific bands were absent in all wheat-rye addition lines, although the presence of rye chromosomes, in all wheat/rye addition lines, was confirmed using both molecular (PCR amplification of rye-specific pSc200 sequence) and cytogenetic (Genomic In Situ Hybridization, GISH, using rye total genomic DNA as probe) approaches. Wheat-origin bands absent in triticale were, however, present in the wheat/rye addition lines. All rye-specific bands were eliminated in the wheat-rye addition lines. The amplification of internal segments of a REMAP rye-specific band confirmed their presence in the triticale and their elimination in wheat/rye addition lines. The results obtained suggest that reduced amounts of introgressed rye chromatin in wheat-rye chromosome addition lines presents an elevated magnitude of sequence modification over that observed in triticale. This understanding of remodeling events involved in genome adjustment to new nuclear environments will certainly contribute to the establishment of a fundamental basis to develop sustained breeding policies involving small amounts of rye chromatin introgressed into wheat.