Discrimination of the closely related A and D genomes of the hexaploid oat Avena sativa L.

Abstract

A satellite DNA sequence, As120a, specific to the A-genome chromosomes in the hexaploid oat, Avena sativa L., was isolated by subcloning a fragment with internal tandem repeats from a plasmid, pAs120, that had been obtained from an Avena strigosa (As genome) genomic library. Southern and in situ hybridization showed that sequences with homology to sequences within pAs120 were dispersed throughout the genome of diploid (A and C genomes), tetraploid (AC genomes), and hexaploid (ACD genomes) Avena species. In contrast, sequences homologous to As120a were found in two A-genome species (A. strigosa and Avena longiglumis) and in the hexaploid A. sativa whereas this sequence was little amplified in the tetraploid Avena murphyi and was absent in the remaining A-and C-genome diploid species. In situ hybridization of pAs120a to hexaploid oat species revealed the distribution of elements of the As120a repeated family over both arms of 14 of 42 chromosomes of this species. By using double in situ hybridization with pAs120a and a C genome-specific probe, three sets of 14 chromosomes were revealed corresponding to the A, C, and D genomes of the hexaploid species. Simultaneous in situ hybridizations with pAs120a and ribosomal probes were used to assign the SAT chromosomes of hexaploid species to their correct genomes. This work reports a sequence able to distinguish between the closely related A and D genomes of hexaploid oats. This sequence offers new opportunities to analyze the relationships of Avena species and to explore the possible evolution of various polyploid oat species.

Genomic and polyploid evolution in genus Avena as revealed by RFLPs of repeated DNA sequences

“…The similarity coefficients were consistently higher in the RFLP analysis (Nocelli et al,1999). Linares et al (1998) described molecular structure and chromosomal organization of the As120a repeated sequence isolated from the A. strigosa genome. The nucleotide sequence determination showed that the fragment was composed of a tandemly repeated DNA sequence adjacent to an unrelated sequence.…”

“…The D genome of the hexaploids is considered to have substantial similarities with the A genome based on GISH results (Chen and Armstrong, 1994;Jellen et al, 1994;Hayasaki et al, 2000). On the other hand, discrimination of the closely related A and D genomes is possible using an A genomespecific AS120a sequence (Linares et al, 1998). The AC1 (A. maroccana) and AC2 tetraploid (A. murphyi) are always grouped with the ACD hexaploids.…”

“…Primer sequences Primer sequences were taken from published nucleotide sequence data of avenin, prolamine (Shotwell et al, 1990) and 12S globulin (Shotwell et al, 1990), seed storage proteins of A. sativa L. and a satellite DNA sequence, As120a, specific to the A genome of A. sativa and A. strigosa (Linares et al, 1998) in a DNA database (GeneBank, http://www.genome.ad.jp/dbget-bin). The primer sequences used for the detection of polymorphism of PCR-RFLPs in Avena species are listed in Table 2.…”

Organization and evolution of highly repeated satellite DNA sequences in plant chromosomes

“…The A genome-specific repetitive family As120a isolated from the diploid species A. strigosa (As) consists of tandem arrays of 114-bp monomeric units (Linares et al, 1998). The As120a homologous sequences labeled only 14 chromosomes of the hexaploid A. sativa genome with a hybridization pattern similar to that of A. strigosa chromosomes.…”

“…The satellite repeat thus allowed a distinction to be made between the otherwise closely related A and D genomes in the hexaploids. The lack of in situ hybridization of this satellite repeat to AACC tetraploids A. maroccana and A. murphyi suggests that a great genomic reorganization of As120a satellite sequences has occurred in the present day AACC tetraploids, probably by deletion events (Linares et al, 1998).…”