A recent publication demonstrated linkage between the 5S and 26S rDNA genes in a liverwort (Marchantia) and a moss (Funaria). No linkage was detected in a green alga (Chlamydomonas), a gymnosperm (Pinus) and an angiosperm (Oryza), hence it was suggested that the colocalization of the 5S and 45S rDNA repeat occurred via an insertion event (transposon-mediated?) within bryophytes. Using primers specific to the 26S and 5S rDNA genes, we conducted a PCR survey of greater than 60 species representing all major land plant lineages. Given that longer amplicons may not always be recovered with standard PCR methods, lack of a PCR product is not definitive evidence for lack of linkage. Despite this, PCR products of varying sizes were obtained from approximately 20 species. These products were cloned and to date some have been sequenced and their identity as IGS (intergenic spacer) confirmed by noting the presence of the 26S rDNA (ca. 200 bp, 3 end) and 5S rDNA (ca. 30 bp, 5 end). To date, the following are confirmed to possess a linked 26S and 5S rDNA: a charophyte (Nitella), a hornwort (Megaceros), liverworts (Conocephalum, Monoclea), a moss (Sphagnum), and a fern (Botrychium). The presence of linkage in a charophyte and a fern thus indicate that colocalization is not a feature unique to bryophytes but occurs more widely among land plants than previously reported.

Key words: 5S rDNA, IGS, intergenic spacer, land plants, nuclear ribosomal DNA