Molecular diversity and physical mapping of 5S rDNA in wild and cultivated oat grasses (Poaceae: Aveneae).

5S rDNA repeats studied in five genera of Aveneae have lengths between 285 and 329 bp (Avena sativa, Avena macrostachya, 26 species of Helictotrichon, Pseudarrhenatherum longifolium, Lagurus ovatus, and Trisetum spicatum). In only a single species (Helictotrichon aetolicum) an additional repeat of 456 bp occurs infrequently. Variation is largely due to insertions or deletions in the nontranscribed spacer as determined from sequences of 163 independent clones. The 5S gene of the Aveneae studied is conserved in length and sequence except for Helictotrichon bromoides and Helictotrichon marginatum in which duplications occur at two different sites. This new type of duplication and all duplications reported to date in 5S genes of angiosperms are shown to center on defined palindromic sequences. The "uncommon" 5S gene sequences detected in some Aveneae are not necessarily nonfunctional as pseudogenes because the essential features of the internal control region are maintained even after such duplication events. In each instance such gene sequences have spacers with unmodified structure, indicating that change in gene sequence is not necessarily coupled with change in adjacent spacers. The value of 5S spacer sequences for genomic identifications in Aveneae is exemplified in A. macrostachya (perennial), A. sativa (annual), and several diploid taxa of the genus Helictotrichon.

Distribution and complex organization of satellite DNA sequences in Aveneae species.

Distribution, organization, and molecular analysis of four unrelated satellite DNA components in Aveneae species are described. Highly repeated DNA elements were cloned from Helictotrichon convolutum (CON1 and CON2) and Helictotrichon compressum (COM1 and COM2). The lengths of the repeat monomers are 365 bp (CON1), 562 bp (CON2), 346 bp (COM1), and 476 bp (COM2). Similar repeats were detected by dot blots, Southern blots, and by DNA sequencing in other species of the genus Helictotrichon, in Aveneae species, and in species of the tribes Andropogoneae and Oryzeae. All four satellite DNAs are differently distributed in the taxonomic groups mentioned above. Remarkably, the longer elements are built up in a complex pattern of either shorter subrepeats arranged in tandem (COM2) or by duplications inserted into an original 369-bp element (CON2). Shorter representatives, 190 bp, similar to CON1 elements occur in Holcus species. In Koeleria species, COM1-related repeats are only 180 bp in length. No similarity was found among the sequences CON2, COM1, and COM2 or with sequences of other repetitive DNA elements of the grasses, but CON1 shows sequence similarity to an A genome specific repetitive DNA of Oryza (rice).

Characterization of a highly repeated DNA component of perennial oats (Helictotrichon, Poaceae) with sequence similarity to a A-genome-specific satellite DNA of rice (Oryza).

The taxonomic relationships among perennial oats (Helictotrichon Besser ex Schultes & Schultes, Aveninae, Aveneae, Poaceae) have been studied using highly repeated satellite DNA as a molecular marker. Highly repetitive sequences were isolated from restriction endonuclease digests of nuclear DNA of Helictotrichon convolutum, and satellite repeats (approximately 365 bp in length) were cloned, sequenced and compared among each other. They exhibited an intraspecific sequence variability of 6-9%. This satellite DNA, CON1, is differentially distributed within the genus Helictotrichon. In species of the subgenus Helictotrichon a high copy number is detectable, whereas in representatives of the subgenera Pratavenastrum and Pubavenastrum the number of copies per genome is rather low. Surprisingly, the satellite DNA repeat CON1 shows 74% sequence similarity to an A-genome specific repetitive DNA of Oryza (rice).