Within- and between-individual length heterogeneity of the rDNA-IGS in Miscanthus sinensis var. glaber (Poaceae):: Phylogenetic analyses

The variability in the intergenic spacer (IGS) region between 17S and 25S rRNA genes of ribosomal DNA (rDNA) gene family was surveyed in Miscanthus sinensis var. glaber. Length heterogeneity, with sizes from 1782 to 2212 base pairs, of the IGS resulted from the variation of copy numbers of the A and B subrepeats. These repeated elements were located upstream of the presumptive polymerase I promoter, which was the region corresponding to the nontranscribed spacer (NTS). Length heterogeneity was detected both within and between individuals of Miscanthus sinensis var. glaber. Neighbor-joining analyses of repetitive A elements indicated that both unequal crossing-over and preferential conversion may have affected the hot-spot regions of the IGS in concert. Within-individual polymorphism and the reconstructed phylogeny suggested that interspecific hybridization has also contributed to length heterogeneity.