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Abstract Detail



Genetics Section

Jang, Tae-Soo [1], Parker, John [2], Weiss-Schneeweiss, Hanna [3].

B-chromosomes in Prospero autumnale complex (Hyacinthaceae): structural polymorphisms and distinct repeat composition suggest their recurrent origin and ongoing evolution.

B-chromosomes are supernumerary elements of the genome, which do not recombine with the regular A-complement chromosomes and follow their own evolutionary trajectory. Recent analyses of B-chromosomes in rye revealed that they are composed of various parts of the A-chromosomes and organellar DNA, and contain significant amounts of repetitive DNA, either A-chromosome specific or evolved de novo B-specific repeats. One interesting system in which to analyze B-chromosome origin, composition, and evolution is chromosomally very variable Prospero autumnale complex (Hyacinthaceae). Four main diploid cytotypes (AA, B7B7, B6B6, and B5B5) with different basic chromosome numbers and distinct karyotypes described in the P. autumnale complex produce a myriad of auto- and allopolyploids. B-chromosomes (Bs) are present both on diploid (genomes A, B7, B6) and polyploid levels. Bs exhibit high levels of polymorphisms in Prospero ranging from their basic morphology (acrocentric, metacentric, or submetacentric) to sequence composition. Fluorescence in situ hybridization (FISH) with 5S and 35S rDNA and novel tandem repeat satellite DNA PaB6 as probes revealed large variation in copy number and localization of those repeats in B-chromosomes, both among and within some cytotypes. B-chromosomes in diploids are usually devoid of 35S rDNA and 5S rDNA, except for one individual, which possesses Bs enriched in 35S rDNA. In contrast, Bs in polyploid individuals are often rich in 5S rDNA repeats, with copy number increasing with the ploidy level. No significant amount of plastid DNA has been detected in B-chromosomes. New satellite DNA PaB6 highly amplified in pericentric regions of regular A-chromosomes of B6B6 cytotype and present in lower copy numbers in all other cytotypes, has been mapped to the pericentromeric and/or subtelomeric regions of Bs in nearly all analyzed individuals, regardless of their ploidy level and PaB6 content in their A-chromosomes. Copy number of PaB6 in Bs increased with ploidy level and often spread over whole Bs, similarly to 5S rDNA. At least ten different combinations of 5SrDNA, 35S rDNA, and satellite DNA PaB6 distribution have been observed in B-chromosomes. We propose that Bs in various cytotypes of P. autumnale complex originate independently and perhaps recurrently as a byproduct of frequent other genomic rearrangements of A-complement chromosomes. Their evolution via accumulation of various repeats and thus establishment might be ongoing, but more dynamic in polyploids.

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1 - Department of Systematic and Evolutionary Botany, University of Vienna, Rennweg 14, Vienna, A-1030 , Austria
2 - Cambridge University Botanic Garden, Cambridge, CB2 1JF, UK
3 - Department of Systematic and Evolutionary Botany, University of Vienna, Rennweg 14, Vienna, A-1030 , Austria

Keywords:
B-chromosomes
Prospero autumnale complex
FISH.

Presentation Type: Oral Paper:Papers for Sections
Session: 6
Location: Marlborough B/Riverside Hilton
Date: Monday, July 29th, 2013
Time: 10:45 AM
Number: 6008
Abstract ID:248
Candidate for Awards:None


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