Repetitive DNA elements as a major component of plant genomes

A major part of the nuclear genome of most plants is composed of different repetitive DNA elements. Studying these sequence elements is essential for our understanding of the nature and consequences of genome size variation b etween different species, and for studying the large-scale organization and evolution of plant genomes. Sugar beet (Beta vulgaris L.) is an important crop and a suitable model for such investigations: with a genome size of 0. 8 pg 1C (760 Mbp) it contains significant amounts of all major groups of re petitive sequences among its nine chromosome pairs, but analysis is not com plicated by polyploidy or the huge size of some genomes, and there are valu able genetic data, recombinant DNA libraries and wild relatives to compleme nt studies of sequence contribution to genome size in sugar beet. A sophist icated understanding of the structure of the genome will provide valuable d ata about the major factors responsible for genome size variation, useful a ids in the development of a molecular understanding of genome evolution, an d perhaps indicate strategies for crop improvement. Using molecular and cyt ological approaches, we have characterized a range of differentially organi zed repetitive DNA sequence elements from the genomes of cultivated and wil d beet species, leading to an extensive model of the repetitive DNA, its or ganization and evolution. (C) 1998 Annals of Botany Company.