Begoña Fernández-Calvín

High molecular weight glutenin subunit variation in the Sitopsis section of Aegilops: implications for the origin of the B genome of wheat

Variation in high molecular weight (HMW) glutenin subunit composition among Aegilops species of the Sitopsis section, namely Ae. bicornis, Ae. longissima, Ae. sharonensis, Ae. searsii and Ae. speltoides was investigated using one-dimensional, as well as two step one-dimensional (2S-1D), sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). The presence of three glutenin bands in several accessions of Ae longissima and Ae. sharonensis seems to be evidence for the existence of at least three active genes, called x, y and z, controlling the synthesis of the high molecular weight glutenins in the genome S of Aegilops. From comparisions between the glutenin patterns found in the species analysed and those bands observed for the B genome of hexaploid wheat, it can be concluded that Ae. bicornis9 Ae. longissima and Ae. sharonensis are unlikely donors of the B genome, mainly because of the presence of specific glutenin markers that were absent in wheat. Ae. searsii and Ae. speltoides showed glutenin subunits that moved within the range of those of B, but Ae. speltoides is the only species that could explain the variablity for HMW subunits previously described for the B genome of wheat, and therefore it cannot be excluded as a possible donor of this genome.

Relationship between the levels of wheat-rye metaphase I chromosomal pairing and recombination revealed by GISH

The metaphase I and anaphase I stages of meiosis of wheatxrye hybrids carrying theph1b mutation were analyzed by genomic in situ hybridization. This technique allows distinction between three different types of wheat-rye associations in metaphase I configurations as well as detection of wheat-rye recombinant chromosomes in anaphase I cells. The frequency of associations between wheat and rye chromosomes greatly exceeded the level of wheat-rye recombination found in the three hybrids examined. Extremely distal associations, which account for about 50% of the total wheat-rye metaphase I chromosomal pairing, can explain such a discrepancy between metaphase I and anaphase I data. It is further discussed whether these associations reflect very distally located chiasmata or nonchiasmatic pairing. The sizes of the segments exchanged in wheat-rye recombinant chromosomes provide cytological evidence that wheat-rye recombination is restricted to the distal chromosomal regions.

Meiotic pairing in wheat-rye derivatives detected by genomic in situ hybridization and C-banding — A comparative analysis

Meiosis of triticalextetraploid rye hybrids (genome constitution ABRRR) was analysed by genomic in situ hybridization (GISH) and C-banding. The results obtained reveal a considerable difference between these techniques with regard to their efficiency in detecting any type of pairing, either homologous or homoeologous. Thus the percentage of pollen mother cells containing wheat/rye homoeologous associations determined by C-banding and GISH was 2.5 and 9.2, respectively. Such a discrepancy can be ascribed to a certain proportion of wheat/rye associations not being identified by C-banding. The potential and limitations of the two techniques for meiotic analysis are discussed.

Relationship between pairing frequencies and genome affinity estimations in Aegilops ovata × Triticum aestivum hybrid plants

Meiotic associations at metaphase I have been analysed in Aegilops ovata × Triticum aestivum hybrid plants (genome constitution ABDUM) with low and high homoeologous pairing by using C-banding. Five different types of meiotic associations involving Aegilops and wheat genomes were identified. Pairing affinities between Aegilops and wheat genomes have been analysed from meiotic associations at metaphase I in low and high homoeologous pairing hybrid plants as well as from different meiotic configurations (bivalents and multivalents) in those hybrids with a high pairing mutant (phlb). Those kinds of distinguishable associations revealed the same relative order: AD-UM > A-D > U-M > AD-B > UM-B in both low and high homoeologous pairing hybrids. The mean number of associations per total associations (relative contribution) for the different distinguishable types of pairing was well maintained among hybrids with different levels of pairing (low and high) as well as in different meiotic configurations (bivalents and multivalents) in the high pairing plants. These results seem to indicate that the affinities expressed between the genomes that are in competition for pairing are independent of the meiotic configurations considered and on the level of pairing analysed.

Chromosomal differentiation in Helianthus annuus var. macrocarpus : heterochromatin characterization and rDNA location

The 2n = 34 chromosomes of the inbred line HA89, and the Flamme and Mirasol hybrids of Helianthus annuus var. macrocarpus possess centromeric heterochromatin as established by Giemsa C-banding. This heterochromatin can not be differentiated by fluorochromes such as DAPI or Chromomycin A3, with selective affinity for specific DNA base pairs. This situation probably results from either a balanced AT/GC composition of the involved repeat or the existence of alternating repetitive sequences of opposite base pair composition in these heterochromatic areas. However, there is also heterochromatin associated with the secondary constrictions on three pairs of chromosomes. This heterochromatin appears to be GC-rich according to its response to the fluorochrome treatments, thus indicating heterochromatin heterogeneity in H. annuus. Silver staining reveals the existence of active NORs associated with these secondary constrictions. In situ hybridization with an rDNA probe confirms these results and makes the existence of other inactive rDNA sites unlikely. These results are relevant to evolutionary and breeding studies on sunflowers.

Comparative analysis of the meiotic effects of wheat ph1b and ph2b mutations in wheat×rye hybrids

Abstract Wheat-wheat and wheat-rye homoeologous pairing at metaphase I and wheat-rye recombination at anaphase I were examined by genomic in situ hybridization (GISH) in wild-type (Ph1Ph2) and mutant ph1b and ph2b wheat×rye hybrids. The metaphase-I analysis revealed that the relative contribution of wheat-rye chromosome associations in ph2b wheat×rye was similar to that of the wild-type hybrid genotype but differed from the effect of the ph1b mutation. The greater pairing promotion effect of the ph1b mutation appears to be relatively more on distant homoeologous partner metaphase-I associations, whereas the lower promoting effect of ph2b is evenly distributed among all types of homoeologous associations. This finding reveals that distinct mechanisms are involved in the control of wheat homoeologous pairing by the two Ph genes. The frequency of wheat-rye recombination calculated from anaphase-I analysis was lower than expected from the metaphase-I data. A greater discrepancy was found in ph2b than in ph1b wheat×rye hybrids, which may suggest a more distal chiasma localization in the former hybrid genotype.

Wolbachia infection in the Chorthippus parallelus hybrid zone: evidence for its role as a reproductive barrier.

Abstract Chorthippus parallelus parallelus (Cpp) and Chorthippus parallelus erythropus (Cpe) are two grasshopper subspecies whose distributions overlap in the Pyrenees, where they form a hybrid zone at those points where the topography and their ecological requirements allow. This hybrid zone is a consequence of secondary contact between endemic Iberian (Cpe) and continental European populations (Cpp) that expanded after the most recent glaciations from the refugia in which they had diverged genetically in allopatry. The morphological, physiological, genetic and behavioral differences between these subspecies (and their natural and laboratory-reared hybrids) have been intensively studied in recent years, for which reason this hybrid zone is considered a singular model in evolutionary biology. These studies reveal a complex pattern of factors involved in the origin, structure and maintenance of the hybrid zone. They offer an excellent panorama of evolution “in action”. Wolbachia is a genus of obligate endosymbiont bacteria that induce changes in the reproduction of arthropods and nematodes. In previous studies we have reported the existence of these bacteria in individuals and populations of Chorthippus parallelus. Now we show that they produce a significant reproductive barrier in this hybrid zone, implying, as proposed elsewhere, that Wolbachia may be involved in speciation phenomena.

Metaphase I bound arms frequency and genome analysis in wheat-Aegilops hybrids : 1. Ae. variabilis-wheat and Ae. kotschyi-wheat hybrids with low and high homoeologous pairing.

SummaryMeiotic associations of different wheat-Aegilops variabilis and wheat-Ae. kotschyi hybrid combinations with low and high homoeologous pairing were analyzed at metaphase I. Five types of pairing involving wheat and Aegilops genomes were identified by using C-banding. A genotype that seems to promote homoeologous pairing has been found in Ae. variabilis var. cylindrostachys. Its effect is detectable in the low pairing hybrids but not in the high ones. Pairing affinity has been analyzed on the basis of metaphase I associations in the low and high homoeologous pairing hybrids, and in bivalents and multivalents in the high pairing hybrids. The results indicate that the amount of bound arms of each type of identifiable association relative to the total associations formed (relative contribution) was not maintained, either between the different levels of pairing (low and high) or between different meiotic configurations (bivalents and multivalents). These findings seem to indicate that quantifications of genomic relationships based on the amount of chromosome pairing at metaphase I must be carefully done in this type of hybrid combinations.

Metaphase I-bound arms frequency and genome analysis in wheat-Aegilops hybrids. 3. Similar relationships between the B genome of wheat and S or S l genomes of Ae. speltoides, Ae. longissima and Ae. sharonensis

The meiotic behaviour of Triticum aestivum × Aegilops speltoides, T. aestivum × Ae. sharonensis and T. aestivum × Ae. longissima tetraploid hybrids (genome constitution ABDS, ABDSl, and ABDSl, respectively) has been analysed by the C-banding technique. Of the six types of pairing normally occurring, at metaphase I three were recognized: A-D, AD-BS/AD-BSl and B-S/B-Sl. The relative order observed in the low pairing hybrid, A-D> B-Sl>AD-BSl, as well as that found in high-pairing ‘Chinese Spring’ × Ae. speltoides hybrids, A-D>AD-BS>ß-S, revealed the existence of preferential pairing patterns among the different genomes that are in competition. In all of the hybrids analysed the mean number of bound arms per cell for the A-D type was significantly higher than the mean number of associations between the B and S/Sl genomes. Usually the relative contribution of each type of pairing is maintained among hybrids with different Aegilops species. These results indicate that the genomes of Ae. speltoides, Ae. sharonensis and Ae. longissima show a similar affinity with the genomes of hexaploid wheat; therefore none of these species can be considered to be a distinct donor of the B genome of wheats.

Metaphase-I bound-arm frequency and genome analysis in wheat-Aegilops hybrids. 2. Cytogenetical evidence for excluding Ae. Sharonensis as the donor of the B genome of polyploid wheats.

SummaryGenome affinities were analyzed at meiosis in C-banded metaphase-I cells of wheat x Ae. Sharonensis hybrid plants. The results showed that the most frequent type of pairing occurred between chromosomes of the A and D genomes in all plants, as well as in cells with different numbers of associations. These findings clearly indicated that Ae. Sharonensis can be excluded as the donor of the B genome of wheat.