The close relationship between the A and B genomes in Avena L. (Poaceae) determined by molecular cytogenetic analysis of total genomic, tandemly and dispersed repetitive DNA sequences
Journal
Annals of Botany
Date Issued
February 1997
DOI
10.1006/anbo.1996.0312
Abstract
The genus Avena L. (Poaceae) consists of diploid, tetraploid, and hexaploid species, with the B genome known only in tetraploid species and the D genome in the hexaploid species. DNA:DNA in situ hybridization, using total genomic DNA from diploid Avena strigosa Schreb. (A8 genome) as a probe, labelled all 28 chromosomes of the AB tetraploid Avena vaviloviana (Malz.) Mordv. strongly and uniformly, revealing the close relationship between these two genomes. Comparison of patterns of size-separated DNA restriction fragments between the diploid A. strigosa and the tetraploid A. valviloviana, using 32 different restriction enzymes, revealed no differences. Southern hybridization using total AB genomic DNA as a probe also gave no differences in banding patterns between the two genomes, even when a large excess of A genomic DNA was used as a block. From an A. vaviloviana genomic library, 1800 colonies were blotted and probed sequentially with A and AB genomic DNA, but no colony was identified to be B genome specific DNA digests of AB genome tetraploids with restriction enzyme HaeIII gave a strong band at 4.2 kb. Clone pAbKB3, derived from the 4.2 kb band, was found to be part of a Tyl-copia-like retrotransposon present in A and B genome chromosomes. Cloned rRNA genes were used for in situ hybridization and showed that diploid A. strigosa has four major sites for 18S-25S rDNA and two pairs of sites for 5SrDNA (pairs on the same satellited chromosome, on different chromosome arms), while 4x A. vaviloviana has eight major sites for 18S-25S rDNA and four pairs of sites for 5S rDNA (pairs on the same satellited chromosome, on different chromosome arms). A repetitive sequence from rye pSc119.2, showed dispersed hybridization, while the telomeric sequence in clone pLT11 hybridized to telomeres. Again no discrimination was possible between A and B genome chromosomes. The molecular similarities between the diploid A. strigosa and the barbara group tetraploids clearly indicate that the barbara group of tetraploids arose from A8 diploids through autotetraploidization.