PIKE, LEE M.1*, SEAN A. WHITCOMB2, and DANIEL L. NICKRENT2. 1Department of Biological Sciences, East Tennessee State University, Johnson City, TN 37614; 2Department of Plant Biology and Center for Systematic Biology, Southern Illinois University, Carbondale, IL, USA 62901-6509. - A Survey of Linkage Between Nuclear 5S and 26S rDNA in Land Plants.
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