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 r RNA genes of ribosomal DNA (rDNA) gene family was surveyed in Miscanthus si nensis 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 presump tive polymerase I promoter, which was the region corresponding to the nontr anscribed spacer (NTS). Length heterogeneity was detected both within and b etween individuals of Miscanthus sinensis var. glaber. Neighbor-joining ana lyses of repetitive A elements indicated that both unequal crossing-over an d 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.