AOBPreview originally published online on May 23, 2005
Annals of Botany 2005 96(2):191-200; doi:10.1093/aob/mci168
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Localization of the 5S and 45S rDNA Sites and cpDNA Sequence Analysis in Species of the Quadrifaria Group of Paspalum (Poaceae, Paniceae)
1 Laboratory of Genetics, Department of Plant Biology, Facultad de Agronomía, Universidad de la República, Av. E. Garzón 780 CP12900, Montevideo, Uruguay, 2 Embrapa Recursos Genéticos e Biotecnologia, Parque Estação Biológica, Brasília DF 70770-900, Brazil, 3 Department of Botany, CCB, Federal University of Pernambuco, Rua Nelson Chaves s/n, 50670-420, Recife, Pernambuco, Brazil and 4 Florida Museum of Natural History, Dickinson Hall, University of Florida, Gainsville, FL 32611-7800, USA
* For correspondence. E-mail mazzella{at}fagro.edu.uy
Received: 6 November 2004 Returned for revision: 10 February 2005 Accepted: 30 March 2005 Published electronically: 23 May 2005
• Background and Aims The Quadrifaria group of Paspalum (Poaceae, Paniceae) comprises species native to the subtropical and temperate regions of South America. The purpose of this research was to characterize the I genomes in five species of this group and to establish phylogenetic relationships among them.
• Methods Prometaphase chromatin condensation patterns, the physical location of 5S and 45S rDNA sites by fluorescence in situ hybridization (FISH), and sequences of five chloroplast non-coding regions were analysed.
• Key Results The condensation patterns observed were highly conserved among diploid and tetraploid accessions studied and not influenced by the dyes used or by the FISH procedure, allowing the identification of almost all the chromosome pairs that carried the rDNA signals. The FISH analysis of 5S rDNA sites showed the same localization and a correspondence between the number of sites and ploidy level. In contrast, the distribution of 45S rDNA sites was variable. Two general patterns were observed with respect to the location of the 45S rDNA. The species and cytotypes Paspalum haumanii 2x, P. intermedium 2x, P. quadrifarium 4x and P. exaltatum 4x showed proximal sites on chromosome 8 and two to four distal sites in other chromosomes, while P. quarinii 4x and P. quadrifarium 2x showed only distal sites located on a variable number of small chromosomes and on the long arm of chromosome 1. The single most-parsimonious tree found from the phylogenetic analysis showed the Quadrifaria species partitioned in two clades, one of them includes P. haumanii 2x and P. intermedium 2x together with P. quadrifarium 4x and P. exaltatum 4x, while the other contains P. quadrifarium 2x and P. quarinii 4x.
• Conclusions The subdivision found with FISH is consistent with the clades recovered with cpDNA data and both analyses suggest that the Quadrifaria group, as presently defined, is not monophyletic and its species belong in at least two clades.
Key words: Grasses, Paspalum, Quadrifaria group, cpDNA sequence analysis, molecular evolution, double-target FISH, rRNA genes, karyotype, prometaphase chromatin patterns
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