Abstracts (poster) - Wissenschaft Online

Martina Dadejova, K. Yoong Lim, Roman Matyasek, Andrew Leitch, Ales Kovarik
Developmental activation of silent rRNA genes is associated
with increased transcription activity of rDNA loci in synthetic
hybrids of Nicotiana
The formation of allopolyploid plant is often associated with homogenization and
expression changes of repeated sequences including tandem arrays of units coding for
18-5.8-26S nuclear ribosomal DNA (rDNA). We have studied inheritance and expression
of parental rDNA (nucleolar dominance) in Nicotiana rustica (2n = 4x = 48), which is a
natural 10 000 years-dated allotetraploid between the diploid species N. paniculata (2n
= 2x = 24, maternal P- genome donor) and N. undulata (2n = 2x = 24, paternal U-
genome donor). We also studied synthetic F1 diploid (1n = 2x = 24) and allotetraploid
(2n = 4x = 48) hybrids derived from respective progenitor species. Natural N. rustica
has approx. three times higher number of U-derived genes than expected from gene
additivity due to interlocus homogenization process, in synthetic hybrids structure and
relative amount of P- and U-type units was not altered (Dadejova et al., 2007).
Expression of rDNA (internal transcribed spacers ITS1 and ITS2) loci was examined by
RT-CAPS method. Transcription analysis revealed silencing of P-type units in leaves of
both N. rustica and synthetic hybrids. In roots, calli and floral organs of the synthetic
hybrids the silent P-units were derepressed. Quantitative PCR showed several fold higher
levels of primary ETS-18S-5.8S-26S transcripts in root tips, floral organs and calli than
in leaves.
Several conclusions can be drawn from this study: (i) developmental switches of
nucleolar dominance occur in synthetic Nicotiana hybrids and polyploids with balanced
numbers of parental rRNA genes (ii) uniparental silencing is broken in tissues with
increased transcription of rDNA (iii) no such switches occur in natural N. rustica with
partially homogenized parental units.
Literature
Dadejová M, Lim KY, Sou•ková-Skalická K, Matyášek R, Grandbastien MA, Leitch AR,
Kovarik A. 2007. Transcription activity of rRNA genes correlates with a tendency towards
intergenomic homogenization in Nicotiana allotetraploids. New Phytologist 174: 658-668.
contact:
Mgr. Martina Dadejova
Academy of Sciences
Institute of Biophysics v.v.i.
dadejova@ibp.cz
Kralovopolska 135
CZ-61265 Brno (Czech Republic)