Paleopolyploidy and its impact on the structure and function of modern plant genomes.

Partial or complete genome duplication is a punctuational event in the evolutionary history of a lineage, with permanent consequences for all descendants. Careful analysis of burgeoning cDNA and genomic sequence data have underlined the importance of genome duplication in the evolution of biological diversity. Of singular importance among the consequences of paleopolyploidy is the extensive loss (or degradation beyond recognition) of duplicated genes. Gene loss complicates genome comparisons by fragmenting ancestral gene orders across multiple chromosomes, and may also link genome duplication to speciation. The recent discovery in angiosperms of gene functional groups that are 'duplicationresistant', i.e. which are preferentially returned to singleton status following genome duplications, adds a new dimension to classical views that focus on the potential advantages of genome duplication as a source of genes with new functions. The surprisingly conservative evolution of coding sequences that are preserved in duplicate, suggests still additional new dimensions in the spectrum of fates of duplicated genes. Looking forward, their many independent genome duplications, together with extensive sets of computational and experimental tools and resources, suggest that the angiosperms may play a major role in clarifying the structural, functional and evolutionary consequences of paleopolyploidy.