Meiosis In Interspecific Hybrids Research Articles

Comparative Tyramide-FISH mapping of the genes controlling flavor and bulb color in Allium species revealed an altered gene order

Evolutionarily related species often share a common order of genes along homeologous chromosomes. Here we report the collinearity disruption of genes located on homeologous chromosome 4 in Allium species. Ultra-sensitive fluorescence in situ hybridization with tyramide signal amplification (tyr-FISH) allowed the visualization of the alliinase multigene family, chalcon synthase gene and EST markers on Allium cepa and Allium fistulosum chromosomes. In A. cepa, bulb alliinase, root alliinase (ALL1) and chalcon synthase (CHS-B) genes were located in the long arm but EST markers (API18 and ACM082) were located in the short arm. In A. fistulosum, all the visualized genes and markers were located in the short arm. Moreover, root alliinase genes (ALL1 and AOB249) showed contrast patterns in number of loci. We suppose that the altered order of the genes/markers is the result of a large pericentric inversion. To get insight into the evolution of the chromosome rearrangement, we mapped the bulb alliinase gene in phylogenetically close and distant species. In the taxonomic clade including A. fistulosum, A. altaicum, A. oschaninii and A. pskemense and in phylogenetically distant species A. roylei and A. nutans, the bulb alliinase gene was located on the short arm of chromosome 4 while, in A. cepa and A. schoenoprasum, the bulb alliinase gene was located on the long arm of chromosome 4. These results have encouraging implications for the further tracing of inverted regions in meiosis of interspecific hybrids and studding chromosome evolution. Also, this finding may have a practical benefit as closely related species are actively used for improving onion crop stock.

Analysis of PolA1 intron 19 and Ntag sequences reveals two ancestral lineages in the origin of the Brassica rapa complex and Chinese cabbage (B. rapa var. pekinensis)

SummaryBrassica rapa L. used to be classified into two species, Brassica campestris and B. rapa.These two species can cross with each other, but no molecular marker exists to discriminate between them. Therefore, these two species are now combined into one species, B. rapa. Because nuclear genomes have been genetically recombined through repeated inter-specific hybridisation, most DNA sequences have lost the characteristics unique to each species. Thus, in order to trace an evolutionary lineage, it is important to analyse a DNA sequence that rarely recombines during meiosis in inter-specific hybrids. Sequences of the nineteenth intron of the PolA1 gene in 33 accessions of B. rapa, encoding the largest subunit of RNA polymerase I, showed either short (S; 183 bp) or long (L; 242 bp) type sequences. Nucleotide tag (Ntag) sequences, the protein-coding sequence (ca. 1.2 kb) from exons 19 - 21 of the PolA1 gene, in 20 accessions, were also classified into the same S- or L-types. Detailed sequence analysis showed that 13 single nucleotide polymorphisms (SNPs) in the 5'-half of the Ntag sequence did not recombine between the S- and L-types.These data suggest that two ancestral lineages were present and were probably involved in the origin of Chinese cabbage because accessions of B. rapa var. pekinensis had PolA1 gene sequences of either the S- or L-type, or both. Two accessions of B. napus var. rapifera (2n = 38) showed both the S- and L-types of B. rapa (2n = 20), indicating that this species might be an allotetraploid between the two ancestral lineages, followed by two chromosome deletions.

High‐resolution molecular karyotyping uncovers pairing between ancestrally related Brassica chromosomes

How do chromosomal regions with differing degrees of homology and homeology interact at meiosis? We provide a novel analytical method based on simple genetics principles which can help to answer this important question. This method interrogates high-throughput molecular marker data in order to infer chromosome behavior at meiosis in interspecific hybrids. We validated this method using high-resolution molecular marker karyotyping in two experimental Brassica populations derived from interspecific crosses among B. juncea, B. napus and B. carinata, using a single nucleotide polymorphism chip. This method of analysis successfully identified meiotic interactions between chromosomes sharing different degrees of similarity: full-length homologs; full-length homeologs; large sections of primary homeologs; and small sections of secondary homeologs. This analytical method can be applied to any allopolyploid species or fertile interspecific hybrid in order to detect meiotic associations. This genetic information can then be used to identify which genomic regions share functional homeology (i.e., retain enough similarity to allow pairing and segregation at meiosis). When applied to interspecific hybrids for which reference genome sequences are available, the question of how differing degrees of homology and homeology affect meiotic interactions may finally be resolved.

Species relationships among the wild B genome of Arachis species (section Arachis) based on FISH mapping of rDNA loci and heterochromatin detection: a new proposal for genome arrangement

Arachis hypogaea is an allotetraploid species with low genetic variability. Its closest relatives, all of the genus Arachis, are important sources of alleles for peanut breeding. However, a better understanding of the genome constitution of the species and of the relationships among taxa is needed for the effective use of the secondary gene pool of Arachis. In the present work, we focused on all 11 non-A genome (or B genome sensu lato) species of Arachis recognized so far. Detailed karyotypes were developed by heterochromatin detection and mapping of the 5S and the 18S-25S rRNA using FISH. On the basis of outstanding differences observed in the karyotype structures, we propose segregating the non-A genome taxa into three genomes: B sensu stricto (s.s.), F and K. The B genome s.s. is deprived of centromeric heterochromatin and is homologous to one of the A. hypogaea complements. The other two genomes have centromeric bands on most of the chromosomes, but differ in the amount and distribution of heterochromatin. This organization is supported by previously published data on molecular markers, cross compatibility assays and bivalent formation at meiosis in interspecific hybrids. The geographic structure of the karyotype variability observed also reflects that each genome group may constitute lineages that have evolved through independent evolutionary pathways. In the present study, we confirmed that Arachis ipaensis was the most probable B genome donor for A. hypogaea, and we identified a group of other closely related species. The data provided here will facilitate the identification of the most suitable species for the development of prebreeding materials for further improvement of cultivated peanut.

Pollination systems, hybridization barriers and meiotic chromosome behaviour in Nemesia hybrids

The ability of 13 Nemesia species (six annual and seven perennial) to sexually hybridize was investigated. Six of the perennial Nemesia species investigated were inter-fertile with one another. Two of the annual species, N. macroceras and N. strumosa, were inter-fertile. Thirty three crosses were successful and resulted in viable seeds. The analysis of meiotic chromosome behaviour in interspecific hybrids indicated that Nemesia chromosomes in different parental species were homeologous. No evidence of chromosome inversions or chromosome translocations was observed during meiosis in interspecific hybrids between the six perennial Nemesia species. In the hybrids produced between N. macroceras and N. strumosa, a quadrivalent was observed during meiotic metaphase I, indicating that these two species differ by a reciprocal translocation. A successful hybridization was made between N. anisocarpa (annual) and N. foetans (perennial), producing two triploid hybrids. In the unsuccessful crosses, pollen tubes were observed entering ovaries and ovules, suggesting that post-fertilization barriers were preventing sexual hybridization. Many of these crosses produced nonviable, shrunken, empty seeds, suggesting that endosperm breakdown and embryo abortion prevent interspecific hybridization in unsuccessful crosses. The manipulation of ploidy levels in N. fruticans and N. strumosa and tissue culture of N. strumosa × N. fruticans ovules failed to overcome post-fertilization barriers between these species.

Meiosis in Interspecific Hybrids and Genomic Interrelationships in Guizotia Cass. (Compositae)

Crosses were made between Guizotia abyssinica, G. scabra ssp. schimperi, G. scabra ssp. scabra, G. villosa, and G. zavatiarii. All taxa have 2n = 30. Crosses involving G. zavaltarii failed to set seed when this species was used as the male parent, but produced shrivelled seeds when it served as the female parent. In the rest of the crosses, 36% of the total number of cross-pollinated florets produced apparently well-developed seeds. 57–95% of the pollen mother cells of F1 hybrids contained 15 II at melaphase I. The mciotic abnormalities observed were univalents at mctaphase I and laggards and bridges and fragments at anaphase/telophase I and II. Two plants from crosses between G. abyssinica and G. villosa exhibited cytomixis and spontaneous fusion of pollen mother cells. The mean pollen fertility of the F, hybrids was 31–81%, and that of the parent plants was 92–96%. The results indicated that G. abyssinica and G. scabra ssp. schimperi are more closely related to each other than to the other taxa, that G. scabra ssp. scabra is more closely related to G. villosa than to G. scabra ssp. schimperi, and that G. zavaltarii has relatively low affinity to the rest of the taxa.

Segregation of isoenzyme markers and meiotic pairing control genes in Lolium

The genetic basis of the control system responsible for suppressing the association of homoeologous chromosomes at first metaphase of meiosis in interspecific hybrids of Lolium was investigated by means of cytological and genetical analyses of a test cross between L. temulentum and L. perenne. It is concluded that more than one gene is involved. Linkage to a gene which codes for an Esterase enzyme of low electrophoretic mobility is clearly identified with the possibility that a second gene is associated with another Esterase locus. The phenotypic effect of individual pairing genes in relation to the distance between them and linked markers is discussed.

The Origin and Relationships of Lasthenia burkei (Compositae)

Lasthenia burkei (Compositae) is a narrowly restricted California endemic closely related to L. conjugens and L. fremontii. These three species differ from each other by pappus and phyllary characters and in geographical distribution. All are freely intercrossable, but L. fremontii forms rather sterile artificial hybrids with its two relatives which, in turn, form fairly fertile artificial hybrids with each other. Lasthenia burkei and L. conjugens have homologous chromosomes, four of which are homologous with four of those of L. fremontii. The remaining two chromosomes probably have reciprocal translocations which lead to multivalent formation during meiosis in interspecific hybrids. Pollen viability is restored in most F2 generations, suggesting a close genetic relationship among the three species. The evolutionary relationship among these species may be a linear one with L. burkei occupying an intermediate position between L. fremontii and L. conjugens, although the direction of this linear phylogeny is not certain, or it may be one in which L. burkei has been derived from hybridization between its two relatives. Support for the latter hypothesis comes from the appearance of some individuals in F1 progenies of L. conjugens × L. fremontii that are morphologically indistinguishable from L. burkei (although fairly sterile). The apparently rather simple genetic basis for the morphological characteristics of each of the species in this trio suggests that the morphologically heterogeneous genus Lasthenia may be considerably more homogeneous genetically than might be suspected. Because of the diverse kinds of relationships among these three Lasthenias, possible alternative taxonomies for the group are dependent upon those relationships that a taxonomist wishes to communicate. Nevertheless, the patterns of diversification in this group have led to reaffirmation of an earlier decision that three species should be recognized.

THE ORIGIN AND RELATIONSHIPS OF LASTHENIA BURKEI (COMPOSITAE)

Lasthenia burkei (Compositae) is a narrowly restricted California endemic closely related to L. conjugens and L. fremontii. These three species differ from each other by pappus and phyllary characters and in geographical distribution. All are freely intercrossable, but L. fremontii forms rather sterile artificial hybrids with its two relatives which, in turn, form fairly fertile artificial hybrids with each other. Lasthenia burkei and L. conjugens have homologous chromosomes, four of which are homologous with four of those of L. fremontii. The remaining two chromosomes probably have reciprocal translocations which lead to multivalent formation during meiosis in interspecific hybrids. Pollen viability is restored in most F2 generations, suggesting a close genetic relationship among the three species. The evolutionary relationship among these species may be a linear one with L. burkei occupying an intermediate position between L. fremontii and L. conjugens, although the direction of this linear phylogeny is not certain, or it may be one in which L. burkei has been derived from hybridization between its two relatives. Support for the latter hypothesis comes from the appearance of some individuals in F1 progenies of L. conjugens × L. fremontii that are morphologically indistinguishable from L. burkei (although fairly sterile). The apparently rather simple genetic basis for the morphological characteristics of each of the species in this trio suggests that the morphologically heterogeneous genus Lasthenia may be considerably more homogeneous genetically than might be suspected. Because of the diverse kinds of relationships among these three Lasthenias, possible alternative taxonomies for the group are dependent upon those relationships that a taxonomist wishes to communicate. Nevertheless, the patterns of diversification in this group have led to reaffirmation of an earlier decision that three species should be recognized.

Fertility Relationships and Meiosis of Interspecific Hybrids in Melilotus1

Fertility Relationships and Meiosis of Interspecific Hybrids in Melilotus¹