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22 - Research Preferential elimination of repeated DNA...

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www.newphytologist.org 291 Research Blackwell Publishing, Ltd. Preferential elimination of repeated DNA sequences from the paternal, Nicotiana tomentosiformis genome donor of a synthetic, allotetraploid tobacco K. Skalická 1 , K. Y. Lim 2 , R. Matyasek 1 , M. Matzke 3 , A. R. Leitch 2 and A. Kovarik 1 1 Institute of Biophysics, Academy of Sciences of the Czech Republic, CZ-61265 Brno, Czech Republic; 2 School of Biological Sciences, Queen Mary, University of London, London E1 4NS, UK; 3 Gregor Mendel-Institut, GMI GmbH, Dr Ignaz Seipel-Platz 2, A-1010 Wien, Austria Summary Nicotiana tabacum (tobacco, 2 n = 4 x = 48) is a natural allotetraploid combining two ancestral genomes closely related to modern Nicotiana sylvestris and Nicotiana tomentosiformis . Here we examine the immediate consequences of allopolyploidy on genome evolution using 20 S 4 -generation plants derived from a single synthetic, S 0 plant made by Burk in 1973 (Th37). Using molecular and cytogenetic methods we analysed 14 middle and highly repetitive sequences that together total 4% of the genome. Two repeats related to endogenous geminiviruses (GRD5) and pararetroviruses ( Nto EPRV), and two classes of satellite repeats (NTRS, A1/A2) were partially or completely eliminated at variable frequency (25–60%). These sequences are all from the N. tomentosiformis parent. Genomic in situ hybridization revealed additivity in chromosome numbers in two plants (2 n = 48), while a third was aneuploid for an N. tomentosiformis -origin chromosome (2 n = 49). Two plants had homozygous translocations between chromosomes of the S- and T-genomes. The data demonstrate that genetic changes in synthetic tobacco were fast, targeted to the paternal N. tomentosiformis -donated genome, and some of the changes showed concordance with changes that presumably occurred during evolution of natural tobacco. Key words: allopolyploidy, chromosomal translocation, endogenous viruses, evolution, Nicotiana spp., satellite repeats. New Phytologist (2005) 166 : 291–303 © New Phytologist (2005) doi : 10.1111/j.1469-8137.2004.01297.x Author for correspondence: Ales Kovarik Tel: +42 541 517 178 Fax: +42 541 211 293 Email: [email protected] Received: 25 August 2004 Accepted: 21 October 2004 Introduction In recent years considerable attention has been paid to under- standing genetic events associated with early allopolyploid nucleus formation (for reviews see Rieseberg, 2001; Liu & Wendel, 2003; Osborn et al ., 2003). Studies of natural polyploids indicate that genetic and epigenetic changes are frequently linked with polyploidy, changes that potentially influence the balance of gene expression and metabolism (Soltis et al ., 2003). However, no overall consensus has been reached con- cerning the evolutionary significance of these allopolyploidy- related or -induced changes because of the variability in responses to polyploidy between species.
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