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要旨

Heritable epigenetic marks, such as cytosine methylation, can be sources of phenotypic variation. In order to understand their role in evolution, it is important to ascertain the intrinsic variability and stability of such marks. Previous studies in Arabidopsis thaliana have described and quantified the stability and emergence of DNA methylation variability across multiple generations. The degree of epigenetic variation within an individual plant as well as between individuals from the same generation has, however, remained elusive. We have compared the methylomes of (i) different organ types and (ii) a series of leaves from the same individual as well as of the corresponding leaves from different individuals. Organ type had the greatest effect on methylome variation, while analogous leaves from different individuals were the most similar. Importantly, there appears to be an ordered progression among a series of consecutive leaves from the same plant. Since these were harvested at the same ti me point, these methylation polymorphisms reflect changes in leaf identity, rather than temporal progression of the entire plant. We have also been able to show the effect of methylated transposable elements on gene expression at a organ specific level. In conclusion, we have been able to identify unique patterns that change systematically with leaf development and organ identity, and provide insights on the variability of epigenetic marks in short ti me scales. hundred kbp) with chromosomal rearrangement. To comprehensively characterize the mutations induced by high-LET beams, the genomes of three Ar-ion induced Arabidopsis mutants (LET = 290 keV/μm, 50 Gy) were re-sequenced in the M3 generation. Total mutations, including base substitutions, duplications, in/dels, inversions, and translocations, were detected using three algorithms (SAMtools, Pindel, and BreakDancer). Averages of 30 homozygous mutations and 49.7 heterozygous mutations were detected per genome. All mutants had genomic rearrangements. Of the 22 DNA fragments that contributed to the rearrangements, 19 fragments were responsible for the intrachromosomal rearrangements, and multiple rearrangements were formed in the localized regions of the chromosomes. The interchromosomal rearrangements were detected in the multi ply rearranged regions. These results indicate that the heavyion beams led to clustered DNA damage in the chromosome, and that they have great potential to induce complicated intrachromosomal rearrangements.