Abstract
Advances in recent years have revolutionized our understanding of both the context and occurrence of polyploidy in plants. Molecular phylogenetics has vastly improved our understanding of plant relationships, enabling us to better understand trait and character evolution, including chromosome number changes. This, in turn, has allowed us to appreciate better the frequent occurrence and extent of polyploidy throughout the history of angiosperms, despite the occurrence of low chromosome numbers in some groups, such as in Arabidopsis (A. thaliana was the first plant genome to be sequenced and assembled). In tandem with an enhanced appreciation of phylogenetic relationships, the accumulation of genomic data has led to the conclusion that all angiosperms are palaeopolyploids, together with better estimates of the frequency and type of polyploidy in different angiosperm lineages. The focus therefore becomes when a lineage last underwent polyploidization, rather than simply whether a plant is ‘diploid’ or ‘polyploid’. This legacy of past polyploidization in plants is masked by large-scale genome reorganization involving repetitive DNA loss, chromosome rearrangements (including fusions and fissions) and complex patterns of gene loss, a set of processes that are collectively termed ‘diploidization’. We argue here that it is the diploidization process that is responsible for the ‘lag phase’ between polyploidization events and lineage diversification. If so, diploidization is important in determining chromosome structure and gene content, and has therefore made a significant contribution to the evolutionary success of flowering plants. © 2015 The Authors. Botanical Journal of the Linnean Society published by John Wiley & Sons Ltd on behalf of The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, ●●, ●●–●●.
Highlights
Polyploidy, or whole genome duplication (WGD), is a frequent phenomenon in plants, especially in flowering plants
It has been estimated that c. 15% of angiosperm speciation events involve a change in ploidy and that all flowering plants have experienced at least one WGD episode in their evolutionary history
De Smet et al (2013) documented consistent patterns of gene deletion in neopolyploid genomes, indicating that genes controlling expression and those in balanced macromolecular complexes were preferentially retained. This process of turnover takes time, and almost certainly leads to novel patterns of expression during the removal of extraneous gene copies. It is clear from global analyses of chromosome number and genome size in a phylogenetic context that, despite the current frequency of polyploidization in angiosperms, there is an irrefutable role for diploidization after polyploidization has occurred
Summary
Polyploidy, or whole genome duplication (WGD), is a frequent phenomenon in plants, especially in flowering plants. 15% of angiosperm speciation events involve a change in ploidy (neopolyploidy; Wood et al, 2009) and that all flowering plants have experienced at least one WGD episode in their evolutionary history (palaeopolyploidy; Bowers et al, 2003; Blanc & Wolfe, 2004; Van de Peer, Maere & Meyer, 2009; Jiao et al, 2011). Ferns contain an even greater number of speciation events involving polyploidy (∼31%; Wood et al, 2009). Following allopolyploidy (hybridization involving polyploidy), be a crucial factor in expanding evolutionary innovation versus relative evolutionary stasis?
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