Uniparental loss of ribosomal DNA in the allotetraploid grassZingeria trichopoda(2n= 8)

Abstract

Analysis of the grass Zingeria trichopoda (2n = 8, 2C = 5.3 pg) revealed a dynamic evolution with the following characteristics. (i) Genomic in situ hybridization (GISH) demonstrates that Z. trichopoda evolved from an interspecific hybrid involving a species like contemporary Zingeria biebersteiniana (2n = 4) and a second species with a similar low number of chromosomes. The nucleus of Z. trichopoda is spatially organized at the genome level and the two parental genomes occupy distinct and separate domains of lateral arrangements. (ii) The copy number of the Z. biebersteiniana specific pericentromeric tandem repeat family Zbcen1 is drastically reduced in Z. trichopoda. (iii) GISH in combination with labeled rDNA sequences simultaneously discriminated the two parental genomes and the corresponding 5S and 45S rDNA sites. Hence, following allopolyploidization of Z. trichopoda the Z. biebersteiniana like parental chromosomes probably underwent drastic loss of 45S rDNA. This could have arisen either through the loss of Z. biebersteiniana derived 45S rDNA or through Z. trichopoda genome-wide homogenization of Z. biebersteiniana type 45S rDNA and subsequent elimination of 45S rDNA loci from Z. biebersteiniana derived chromosomes. Finally, 5S rDNA loci are present in both subgenomes of Z. trichopoda and the chromosomal position of these loci is similar for both Z. biebersteiniana and the Z. biebersteiniana like parental genome of Z. trichopoda.

Nucleolar dominance and maternal control of 45S rDNA expression

“…Histone deacetylase Sir2 controls both E-pro transcription [39] and replication timing [47]. Uniparental loss of 45S rDNA was also reported in the allotetraploid grass Zingeria trichopoda [48], allotetraploid Tragopogon (Asteraceae) [49], and allopolyploid yeast Pichia sorbitophila [50]. All these observations from hybrid (allopolyploid) genomes suggest that parent-of-origin effects may be a pervasive feature of rDNA chromatin.…”

Rapid Concerted Evolution of Nuclear Ribosomal DNA in Two Tragopogon Allopolyploids of Recent and Recurrent OriginSequence data from this article have been deposited with the EMBL/GenBank Data Libraries under accession nos. AY458586, AY458588, AY458589, and AY458587

“…For each Glycine (Rauscher et al 2004). Concerted evolution population sampled, we collected seeds from 50 individual may be mediated by locus loss (Kotseruba et al 2003) plants; the seeds from each plant were kept separate. These or interlocus gene conversion (Wendel et al 1995a; Lim seeds were subsequently planted in the greenhouses at Washington State University; plants were grown to maturity and (1953) were cloned using the TOPO TA cloning kit (Invitrogen, Carlsbad, CA).…”

“…The ancestries of both tetraploids were subsequently known to have arisen spontaneously within the past 150 confirmed through flavonoid, isozymic, and DNA studyears: Cardamine schulzii (Urbanska et al 1997), Spartina ies (Ownbey and McCollum 1953;Brehm and Ownanglica (Ainouche et al 2004), Senecio cambrensis, and bey 1965; Roose and Gottlieb 1976; Soltis and Senecio eboracensis (Abbott and Lowe 2004), and Trago- Soltis 1989Soltis et al 1995;Cook et al 1998). pogon mirus and T. miscellus (Ownbey 1950;Soltis et The allotetraploids have not formed in Europe, but are al.…”

“…Most species are diploid (2n ϭ probably did not co-occur in the Palouse prior to the 1920s (the earliest collection, of T. dubius, the diploid parent common to both tetraploid species, is from 1928; Ownbey 1950), T. mirus and T. miscellus cannot be Ͼ quent morphological and cytological (Ownbey and and extant diploids may be misleading with regard to patterns and rates of genetic change. McCollum 1954), isozymic (Roose and Gottlieb 1976; The recent allotetraploids T. mirus and T. miscellus Soltis et al 1995), and DNA (Soltis and Soltis 1989, represent a convenient natural system in which to study 1991; Cook et al 1998) evidence, when considered the early genetic changes associated with allopolyploidialong with geographic distribution, demonstrated that zation. Given their recent origins, their parental genoeach allopolyploid had formed repeatedly.…”

Plant biosystematics with the help of cytology and cytogenetics

“…in Aristolochia, Nicotiana and Avena (Roa and Guerra 2012). In particular, in a Zingeria trichopoda hybrid (2n = 8) the rDNA sequences of one of the parental species have been eliminated (Kotseruba et al 2003). Great intraspecific variability in the number of NOR was repeatedly detected in the genus Allium (Bougourd and Parker 1976;Loidl and Greilhuber 1983;Schubert and Wobus 1985;Jamilena et al 1990;Garrido-Ramos et al 1992).…”