John Innes Center:
In the May 2000 issue of The Plant Cell (12(5):617-636), Prof. Pat Heslop-Harrison at the John Innes Center discusses in depth how technologies such as silico analysis, high throughput DNA and protein studies, digital imaging methods and in vivo methods to study dynamic chromosome structure are helping us understand the behavior, function, and evolution of the chromosome in the nucleus. Even five years ago the model of the chromosome was different from that what we know now. It is only recently that information has come to light about chromatin packaging and three dimensional organization. For a complete understanding of the genome, such information is essential.
Recent studies on the telomeric and centromeric structure have revealed that the repeats are species specific. Differences in the number of copies of the telomere is also species specific. For instance, the chromosome fragment of Beta procumbens, when introduced into the chromosome complement of B. vulgaris, did not show a telomeric sequence like the rest of the parental chromosomes and was therefore lost. Recent studies also have shown that sequence motifs are extremely variable even between different accessions of a species. In floral homeotypic mutants of Arabidopsis, direct correlation between DNA methylation and normal regulation of developmentally important genes was observed. That is to say, different regions of chromosomes were found to have different levels of methylation. One interesting observation mentioned in the article was the evolutionary insertion of a ~270 kb long mitochodrial genome into chromosome two of Arabidopsis.