Genomic and genetic relationships among species of Leymus (Poaceae: Triticeae) inferred from 18S-26S ribosomal genes.

The 18S-26S ribosomal genes in three closely related species of Leymus (Poaceae: Triticeae) were examined using fluorescence in situ hybridization (FISH) and restriction fragment length polymorphism (RFLP). Both approaches revealed a close relationship between L. arenarius (8x = 56, northern European) and L. racemosus (4x = 28, central Eurasian), whereas L. mollis (4x = 28, northern American/Pacific) was distinct. Each species had three homologous pairs of major rDNA loci: a1, a2, and a3 for L. arenarius; m1, m2, and m3 for L. mollis; and r1, r2, and r3 for L. racemosus. Leymus arenarius had in addition three minor loci, a4, a5, and a6. The major loci of L. arenarius and L. racemosus were identical, indicating that the former species could have originated from the latter, via interspecific hybridization and/or polyploidy. The rDNA-RFLPs further indicated relationships of these species to other species of Leymus (L. karellini, 8x = 56 and L. angustus, 12x = 84) and Psathyrostachys (P. fragilis, P. huashanica, P. juncea, and P. lanuginosa, which are all diploids). A phenogram constructed from 20 BamHI, EcoRI, and DraI rDNA fragments revealed closer relationship between the two genera, Leymus and Psathyrostachys, than that among species within a genus.

p53 abnormality and chromosomal instability in the same breast tumor cells.

To clarify the important role of the tumor-suppressor gene p53 in maintaining genetic integrity, we estimated chromosome instability and staining of overexpressed p53 protein in the same cells of five primary breast carcinomas. The method included both fluorescence immunohistochemistry and fluorescence in situ hybridization (FISH) on sections from formalin-fixed, paraffin-embedded breast cancer tissue. By using a centromeric FISH probe for chromosome 17 on interphase cells in these sections, we showed that cells with abnormal p53 protein expression had a statistically significant higher number of chromosome 17 than did cells with no p53 protein staining in the same samples as well as cells in four other tumor samples with no p53 protein staining. The samples identified positive for p53 abnormality by immunostaining were shown to have p53 mutation by constant denaturing gel electrophoresis analysis and DNA sequencing. These mutated samples were characterized by high DNA index, high S-phase, abnormal karyotype, and aneuploidy. The results strongly implicate p53 mutation as a cause for chromosomal instability and a crucial step in mammary carcinogenesis.

Molecular variation in Leymus species and populations.

Icelandic populations of European lymegrass [Leymus arenarius (L.) Hochst.] were examined using amplified fragment length polymorphism (AFLP) and restriction fragment length polymorphism (RFLP) of the major ribosomal genes (18S-5.8S-26S rDNA), in comparison with Alaskan populations of its closely related species L. mollis (Trin.) Pilger. The AFLP profiles emerged as two distinct entities, clearly separating the two species, and based on species-specific bands it was simple to distinguish these two morphologically similar species. The rDNA-RFLPs also differentiated the species. Within species, the Icelandic L. arenarius was more homogeneous than the Alaskan L. mollis, and its variation was dispersed over geographically different populations, suggesting a common gene pool. The variation among the Alaskan L. mollis was more extensive and its interrupted pattern may be the result of gene introgression at subspecies level. Within a 40-year-old population of L. mollis established in Iceland from Alaskan material, the molecular profiles separated old and new genotypes. Both AFLP and rDNA revealed the new genotypes to be extremely similar. This rapid change in allele frequency is thought to be the result of adaptation to a new environment.

Meiosis of wheat x lymegrass hybrids.

Meiosis was examined in pollen mother cells of F1 hybrids made from crosses between wheat (Triticum aestivum) and lymegrass (Leymus arenarius and L. mollis). Fluorescence genomic in situ hybridization detected pairing between wheat and lymegrass chromosomes during prophase I and metaphase I. Such pairing, when resulting in bivalent formation, was likely to yield correct disjunction, and hence intergenomic recombination could be incorporated into the gametes. Bivalents in these hybrids, however, were more frequently formed between chromosomes of the same parental origin. Univalents were common, whereas multivalents were not clearly detected. Meiotic behaviour in some cells was not totally aberrant, and this may have accounted for the presence of normal pollen. The results are discussed in relation to intergenomic pairing, meiotic behaviour in wide-hybrids and genome relationships, including the Leymus genome origin.