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 between 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 repetitive sequences among its nine chromosome pairs, but analysis is not complicated by polyploidy or the huge size of some genomes, and there are valuable genetic data, recombinant DNA libraries and wild relatives to complement studies of sequence contribution to genome size in sugar beet. A sophisticated understanding of the structure of the genome will provide valuable data about the major factors responsible for genome size variation, useful aids in the development of a molecular understanding of genome evolution, and perhaps indicate strategies for crop improvement. Using molecular and cytological approaches, we have characterized a range of differentially organized repetitive DNA sequence elements from the genomes of cultivated and wild beet species, leading to an extensive model of the repetitive DNA, its organization and evolution.