Clarkson, James J. , Chase, Mark W. , Leitch, Andrew R. , Knapp, Sandra .
The long-term effects of polyploidy in Nicotiana: contrasting the fate of nuclear ribosomal loci and single-copy nuclear loci.
Nicotiana (Solanaceae) contains 75 species, approximately half of which are diploid (two sets of chromosomes) and half are allotetraploid (four sets of chromosomes derived from two different diploid progenitors). We have gathered a number of phylogenetic datasets for Nicotiana, each with near-complete species sampling. There are three dataset types 1) plastid (multiple loci) 2) nuclear ribosomal (ITS locus) and 3) single copy nuclear (glutamine synthetase (GS) locus). Phylogenetic trees were calibrated and used for a molecular clock analysis to estimate the ages of the allotetraploids. Chromosome painting revealed that young polyploids (eg. N. tabacum - formed 0.2 million years ago) have the sum of their progenitors ribosomal loci. However, although these loci occur at the same chromosomal positions as in their progenitors the loci have been overwritten by just one progenitor type resulting in the retention of a single ITS copy (concerted evolution). Older polyploids (eg. section Repandae - formed 4.5 mya) do not have the sum of their two progenitor loci and must have undergone locus loss. It seems that over time they have been reduced to an ever-more diploid-like state. In contrast both progenitor types of GS could be sequenced from polyploids of all ages. This suggests that no concerted evolution or progenitor locus loss associated with diploidisation is seen in single-copy nuclear genes. No breaks in the reading frame were observed in either homoeologue of GS, suggesting that they are probably both functional, even in older polyploids. Recent studies in Gossypium have shown that two functional homoeologues can have different expression patterns; some tissues predominantly express one progenitor type and other tissues express the other. Therefore, some form of differential specialisation of the two copies might be the reason that they are retained by polyploids.
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1 - Royal Botanic Gardens, Kew, Jodrell Laboratory, Richmond, Surrey, TW9 3AB, United Kingdom
2 - Queen Mary University of London, School of Biological Sciences, London, E1 4NS, United Kingdom
3 - Natural History Museum, Department of Botany, Cromwell Road, London, SW7 5BD, England
Presentation Type: Oral Paper:Papers for Sections
Location: 182/I K Barber
Date: Monday, July 28th, 2008
Time: 8:45 AM