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1.  Differential amplification of satellite PaB6 in chromosomally hypervariable Prospero autumnale complex (Hyacinthaceae) 
Annals of botany  2014;114(8):1597-1608.
Background and Aims
Chromosomal evolution, including numerical and structural changes, is a major force in plant diversification and speciation. This study addresses genomic changes associated with the extensive chromosomal variation of the Mediterranean Prospero autumnale complex (Hyacinthaceae), which includes four diploid cytotypes each with a unique combination of chromosome number (x = 5, 6, 7), rDNA loci and genome size.
Methods
A new satellite repeat PaB6 has previously been identified, and monomers were reconstructed from next-generation sequencing (NGS) data of P. autumnale cytotype B6B6 (2n = 12). Monomers of all other Prospero cytotypes and species were sequenced to check for lineage-specific mutations. Copy number, restriction patterns and methylation levels of PaB6 were analysed using Southern blotting. PaB6 was localized on chromosomes using fluorescence in situ hybridization (FISH).
Key Results
The monomer of PaB6 is 249 bp long, contains several intact and truncated vertebrate-type telomeric repeats and is highly methylated. PaB6 is exceptional because of its high copy number and unprecedented variation among diploid cytotypes, ranging from 104 to 106 copies per 1C. PaB6 is always located in pericentromeric regions of several to all chromosomes. Additionally, two lineages of cytotype B7B7 (x = 7), possessing either a single or duplicated 5S rDNA locus, differ in PaB6 copy number; the ancestral condition of a single locus is associated with higher PaB6 copy numbers.
Conclusions
Although present in all Prospero species, PaB6 has undergone differential amplification only in chromosomally variable P. autumnale, particularly in cytotypes B6B6 and B5B5. These arose via independent chromosomal fusions from x = 7 to x = 6 and 5, respectively, accompanied by genome size increases. The copy numbers of satellite DNA PaB6 are among the highest in angiosperms, and changes of PaB6 are exceptionally dynamic in this group of closely related cytotypes of a single species. The evolution of the PaB6 copy numbers is discussed, and it is suggested that PaB6 represents a recent and highly dynamic system originating from a small pool of ancestral repeats.
doi:10.1093/aob/mcu178
PMCID: PMC4273535  PMID: 25169019
PaB6; Prospero autumnale; Hyacinthaceae; chromosomal evolution; copy number; differential amplification; fluorescence in situ hybridization (FISH); genome size; pericentric satellite DNA; next-generation sequencing
2.  Evolution of Genome Size in Brassicaceae 
Annals of botany  2005;95(1):229-235.
Background and Aims
Brassicaceae, with nearly 340 genera and more than 3350 species, anchors the low range of angiosperm genome sizes. The relatively narrow range of DNA content (0·16 pg < 1C < 1·95 pg) was maintained in spite of extensive chromosomal change. The aim of this study was to erect a cytological and molecular phylogenetic framework for a selected subset of the Brassicacae, and use this as a template to examine genome size evolution in Brassicaceae.
Methods
DNA contents were determined by flow cytometry and chromosomes were counted for 34 species of the family Brassicaceae and for ten Arabidopsis thaliana ecotypes. The amplified and sequenced ITS region for 23 taxa (plus six other taxa with known ITS sequences) were aligned and used to infer evolutionary relationship by parsimony analysis.
Key Results
DNA content in the species studied ranged over 8-fold (1C = 0·16–1·31 pg), and 4·4-fold (1C = 0·16–0·71 pg) excluding allotetraploid Brassica species. The 1C DNA contents of ten Arabidopsis thaliana ecotypes showed little variation, ranging from 0·16 pg to 0·17 pg.
Conclusions
The tree roots at an ancestral genome size of approximately 1x = 0·2 pg. Arabidopsis thaliana (1C = 0·16 pg; ~157 Mbp) has the smallest genome size in Brassicaceae studied here and apparently represents an evolutionary decrease in genome size. Two other branches that represent probable evolutionary decreases in genome size terminate in Lepidium virginicum and Brassica rapa. Branches in the phylogenetic tree that represent probable evolutionary increases in genome size terminate in Arabidopsis halleri, A. lyrata, Arabis hirsuta, Capsella rubella, Caulanthus heterophyllus, Crucihimalaya, Lepidium sativum, Sisymbrium and Thlaspi arvense. Branches within one clade containing Brassica were identified that represent two ancient ploidy events (2x to 4x and 4x to 6x) that were predicted from published comparative mapping studies.
doi:10.1093/aob/mci016
PMCID: PMC1950721  PMID: 15596470
Arabidopsis; Brassicaceae; ITS phylogeny; DNA content; genome size; chromosome number

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