Genome structure and evolution in the allohexaploid weed Avena fatua L. (Poaceae)

Abstract

Allohexaploid wild oat, Avena fatua L. (Poaceae; 2n = 6x = 42), is one of the world's worst weeds, yet unlike some of the other Avena hexaploids, its genomic structure has been relatively little researched. Consequently, in situ hybridisation was carried out on one accession of A. fatua using an 18S-25S ribosomal DNA (rDNA) sequence and genomic DNA from A. strigosa (AA-genome diploid) and A. clauda (CC-genome diploid) as probes. Comparing these results with those for other hexaploids studied previously: (i) confirmed that the genomic composition of A. fatua was similar to the other hexaploid Avena taxa (i.e., AACCDD), (ii) identified major sites of rDNA on three pairs of A/D-genome chromosomes, in common with other Avena hexaploids, and (iii) revealed eight chromosome pairs carrying intergenomic translocations between the A/D- and C-genomes in the accession studied. Based on karyotype structure, the identity of some of these recombinant chromosomes was proposed, and this showed that some of these could be divided into two types, (i) those common to all hexaploid Avena species analysed (3 translocations) and (ii) one translocation in this A. fatua accession not previously observed in reports on other hexaploid Avena species. If this translocation is found to be unique to A. fatua, then this information, combined with more traditional morphological data, will add support to the view that A. fatua is genetically distinct from other hexaploid Avena species and thus should retain its full specific status.

Intergenomic translocations of polyploid oats (genus Avena) revealed by genomic in situ hybridization.

“…We observed that the terminal A/D translocations in A. fatua occurred on the 1C and 7C. Yang et al (1999) reported that the terminal A/D-C translocations on the 1C, 3C or 4C, and in addition, detected a terminal A/D translocation on each arm of chromosome 7C. In our study, a terminal A/D translocations in A. sterilis was observed on chromosomes 1C and 7C and corresponded to the results of Jellen et al (1994).…”

“…Although both tetraploid species, A. maroccana and A. murphyi were detected the translocation segment on medium length chromosome of seven pairs of C-genome chromosomes, two hexaploid species, A. byzantina (our result) and A. fatua (Yang et al, 1999) were also detected on medium length chromosome. It suggests that the chromosomes with the segment of two hexaploids are conservative.…”

“…A number of authors have attempted to identify individual C-genome chromosomes in hexaploid oats by GISH and FISH (e.g. Chen and Armstrong, 1994;Jellen et al, 1994;Leggett and Markhand, 1995;Yang et al, 1999). Fominaya et al (1995) and Linares et al (1996) performed FISH analysis using a repeated DNA sequence (pAm1) specific to C-genome chromosomes.…”

“…At the moment, the GISH was unable to separate the A-and D-genome chromosomes in hexaploid oats. But absolute discrimination between A/D-and C-genome chromosomes has been demonstrated by several oat workers (Jellen et al, 1994;Chen and Armstrong, 1994;Leggett and Markhand, 1995;Yang et al, 1999). These authors observed small C-genome segments translocated onto A-or D-genome chromosomes (abbreviated as C-A/D translocation) and vice versa (abbreviated as A/D-C) for A-or D-segments translocated onto C-genome chromosomes.…”

FISH Karyotype and GISH Meiotic Pairing Analyses of a Stable Intergeneric Hybrid xBrassicoraphanus Line BB#5

“…Chromosome characterization and genome identification have advanced significantly with the development of molecular cytogenetics through fluorescence in situ hybridization (FISH) and genomic in situ hybridization (GISH) techniques (Capdeville et al, 2008;Fukui, 2005;Hwang et al, 2010Hwang et al, , 2012Levsky and Singer, 2003;Park et al, 2010). Indeed, these methods have been used to investigate genome structure and inter-genomic relationship of hybrid plants (Jellen et al, 1994;Kenton et al, 1993), allopolyploid species (Cao, 2003;Devi et al, 2005;Yang et al, 1999), and recombinant breeding lines (Hwang et al, 2012;Lou et al, 2010;Vasconcelos et al, 2010).…”