Genome rearrangements derived from autopolyploidization in Paspalum sp.

Rapid sequence rearrangements along with alterations in cytosine-directed methylation patterns follow allopolyploid formation in several plant species. The occurrence of similar changes is yet to be examined in detail during the generation of autopolyploids. The objective of this work was to investigate the presence of nascent variation in genome sequence after autopolyploidization in two Paspalum species. The increments of ploidy level were produced either by hybridization involving unreduced gametes or colchicine treatment. Genetic modifications affected 15–23% and 9.55% of the genomic loci in Paspalum rufum and Paspalum notatum, respectively. In all cases the frequency of band loss from the progenitors was significantly higher than that of novel band gain. In random amplified polymorphic DNA (RAPD) experiments the majority of polymorphisms were detected by particular sets of primers, suggesting that repetitive domains were preferentially targeted. Several P. notatum polymorphic fragments were cloned, sequenced and used as probes in genomic hybridization analyses. Some of them corresponded to interspersed middle-repetitive sequences with unknown function. Methylation-sensitive genomic hybridization showed that sequence modifications occurred invariably in cytosine-methylated regions, which remained methylated after polyploidization.