Format: ORAL

Pat Heslop-Harrison1,2, Qing Liu2, Ziwei Wang2, Trude Schwarzacher1,2

1 University of Leicester, Leicester, United Kingdom 2 South China Botanical Garden, Guangzhou, China

Long, single-molecule DNA sequencing shows the organization and structures of rDNA monomers in tandem repeats. Short reads of both 5S and 45S rDNA collapse the arrays during assembly, while older BAC sequences suffer from chaemerism and assembly artefacts. Far from being a continuous array of monomers, we find short deletions, insertions or interruptions in the arrays. Full-length retroelements are found at variable points within some 45S and 5S monomers in the arrays, and there are occasional insertions of uncharacterized sequences. Within monomers, both deletions and short duplications are found. Similar rearrangements have been found in multiple, non-identical, reads, giving evidence for homogenization through unequal crossing-over (and hence duplication of segments of the arrays). The starts of the arrays have been characterized with flanking sequences. Musaceae provides a good model for the comparative study of the rDNA arrays, with long reads available from multiple species, variable chromosome numbers and evolutionary movement of rDNA between chromosomes, independent of other genes. The rDNA is very variable between species, many with one pair sites of 45S rDNA, representing 1% of all the DNA, to Musa beccarii with 3 sites and 5% of the DNA. Monomer lengths are also variable, with the typical length around 400bp found for most 5S monomers but 1056bp in Ensete. The detailed characterization of the arrays shows evolutionary mechanisms and diversity of the ribosomal DNA arrays. Further information and references are given at www.molcyt.com .