Flow cytometry and cytogenetic tools in eucalypts: genome size variation × karyotype stability
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The eucalypts comprise a group of woody plants used in commercial forest plantations owing to their high growth rates, adaptability to various ecological conditions and multiple applications. Despite the enormous amount of molecular data available for eucalypts, a basic understanding of the nature of its genome still requires information regarding the DNA amount in the genus. In this work, we estimated the genome size and base composition of 25 eucalypt species. With a comparative karyotype approach, we aimed to identify possible chromosomal alterations correlated with the genome size variation. Classical cytogenetic and genomic in situ hybridization experiments were conducted for this purpose. The studied species showed genome size ranging from 2C = 0.91 (Corymbia intermedia) to 2C = 1.37 pg (Eucalyptus paniculata) and AT/CG ratios varying from AT = 61.3 (Eucalyptus urophylla) to AT = 62.85% (C. intermedia). Comparative karyotype analysis revealed no remarkable differences in chromosome number (2n = 22) or morphology among eucalypt species despite considerable differences in nuclear DNA content. The genome in situ hybridization method did not distinguish non-homologous chromosomal regions of Eucalyptus baileyana and Corymbia citriodora, despite the difference of 0.45 pg between their genome sizes. The results found in the present work corroborate the consideration of small and dispersed DNA changes as the main cause of genome size variation in eucalypts.
KeywordsEucalyptus Corymbia 2C-value Base composition Chromosome Karyotype
The authors would like to thank the Conselho Nacional de Pesquisa (CNPq, Brazil), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES, Brazil) and Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG, Brazil) for providing financial support for this study. We are also grateful to Dr. Dário Grattapaglia (Plant Genetics Laboratory, Embrapa, Brasília, Brazil), Instituto de Pesquisas Florestais (IPEF, Brazil), Sociedade de Investigações Florestais (SIC, Brazil) and the company Klabin (Brazil) for kindly providing the eucalyptus seeds.
GMAC and CRC designed and conducted classical cytogenetic and flow cytometry experiments. GMAC, CRC and FAFS designed and conducted the GISH experiment. GMAC and CRC wrote the manuscript. All authors participated in the analysis of this study and read the final manuscript.
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