Induction Of Chromosomal Rearrangements Research Articles

Transfer of the ph1b Deletion Chromosome 5B From Chinese Spring Wheat Into a Winter Wheat Line and Induction of Chromosome Rearrangements in Wheat-Aegilops biuncialis Hybrids.

Effective utilization of genetic diversity in wild relatives to improve wheat requires recombination between wheat and alien chromosomes. However, this is suppressed by the Pairing homoeologous gene, Ph1, on the long arm of wheat chromosome 5B. A deletion mutant of the Ph1 locus (ph1b) has been used widely to induce homoeologous recombination in wheat × alien hybrids. However, the original ph1b mutation, developed in Chinese Spring (CS) background has poor agronomic performance. Hence, alien introgression lines are first backcrossed with adapted wheat genotypes and after this step, alien chromosome segments are introduced into breeding lines. In this work, the ph1b mutation was transferred from two CSph1b mutants into winter wheat line Mv9kr1. Homozygous genotypes Mv9kr1 ph1b/ph1b exhibited improved plant and spike morphology compared to Chinese Spring. Flow cytometric chromosome analysis confirmed reduced DNA content of the mutant 5B chromosome in both wheat genotype relative to the wild type chromosome. The ph1b mutation in the Mv9kr1 genotype allowed wheat-alien chromosome pairing in meiosis of Mv9kr1ph1b_K × Aegilops biuncialis F1 hybrids, predominantly with the Mb-genome chromosomes of Aegilops relative to those of the Ub genome. High frequency of wheat-Aegilops chromosome interactions resulted in rearranged chromosomes identified in the new Mv9kr1ph1b × Ae. Biuncialis amphiploids, making these lines valuable sources for alien introgressions. The new Mv9kr1ph1b mutant genotype is a unique resource to support alien introgression breeding of hexaploid wheat.

Machine-learning predicts genomic determinants of meiosis-driven structural variation in a eukaryotic pathogen

Species harbor extensive structural variation underpinning recent adaptive evolution. However, the causality between genomic features and the induction of new rearrangements is poorly established. Here, we analyze a global set of telomere-to-telomere genome assemblies of a fungal pathogen of wheat to establish a nucleotide-level map of structural variation. We show that the recent emergence of pesticide resistance has been disproportionally driven by rearrangements. We use machine learning to train a model on structural variation events based on 30 chromosomal sequence features. We show that base composition and gene density are the major determinants of structural variation. Retrotransposons explain most inversion, indel and duplication events. We apply our model to Arabidopsis thaliana and show that our approach extends to more complex genomes. Finally, we analyze complete genomes of haploid offspring in a four-generation pedigree. Meiotic crossover locations are enriched for new rearrangements consistent with crossovers being mutational hotspots. The model trained on species-wide structural variation accurately predicts the position of >74% of newly generated variants along the pedigree. The predictive power highlights causality between specific sequence features and the induction of chromosomal rearrangements. Our work demonstrates that training sequence-derived models can accurately identify regions of intrinsic DNA instability in eukaryotic genomes.

Induction of chromosome rearrangements in a 4H(4D) wheat-barley substitution using a wheat line containing aPhsuppressor gene

Induction of chromosome rearrangements in a 4H(4D) wheat-barley substitution using a wheat line containing a<i>Ph</i>suppressor gene

Multi-functional T-DNA/Ds tomato lines designed for gene cloning and molecular and physical dissection of the tomato genome.

In order to make the tomato genome more accessible for molecular analysis and gene cloning, we have produced 405 individual tomato (Lycopersicon esculentum) lines containing a characterized copy of pJasm13, a multifunctional T-DNA/modified Ds transposon element construct. Both the T-DNA and the Ds element in pJasm13 harbor a set of selectable marker genes to monitor excision and reintegration of Ds and additionally, target sequences for rare cutting restriction enzymes (I-PpoI, SfiI, NotI) and for site-specific recombinases (Cre, FLP, R). Blast analysis of flanking genomic sequences of 174 T-DNA inserts revealed homology to transcribed genes in 69 (40%), of which about half are known or putatively identified as genes and ESTs. The map position of 140 individual inserts was determined on the molecular genetic map of tomato. These inserts are distributed over the 12 chromosomes of tomato, allowing targeted and non-targeted transposon tagging, marking of closely linked genes of interest and induction of chromosomal rearrangements including translocations or creation of saturation-deletions or inversions within defined regions linked to the T-DNA insertion site. The different features of pJasm13 were successfully tested in tomato and Arabidopsis thaliana, thus providing a new tool for molecular/genetic dissection studies, including molecular and physical mapping, mutation analysis and cloning strategies in tomato and potentially, in other plants as well.

Analysis of chromosomal rearrangements induced by postmeiotic mutagenesis with ethylnitrosourea in zebrafish.

Mutations identified in zebrafish genetic screens allow the dissection of a wide array of problems in vertebrate biology. Most screens have examined mutations induced by treatment of spermatogonial (premeiotic) cells with the chemical mutagen N-ethyl-N-nitrosourea (ENU). Treatment of postmeiotic gametes with ENU induces specific-locus mutations at a higher rate than premeiotic regimens, suggesting that postmeiotic mutagenesis protocols could be useful in some screening strategies. Whereas there is extensive evidence that ENU induces point mutations in premeiotic cells, the range of mutations induced in postmeiotic zebrafish germ cells has been less thoroughly characterized. Here we report the identification and analysis of five mutations induced by postmeiotic ENU treatment. One mutation, snh(st1), is a translocation involving linkage group (LG) 11 and LG 14. The other four mutations, oep(st2), kny(st3), Df(LG 13)(st4), and cyc(st5), are deletions, ranging in size from less than 3 cM to greater than 20 cM. These results show that germ cell stage is an important determinant of the type of mutations induced. The induction of chromosomal rearrangements may account for the elevated frequency of specific-locus mutations observed after treatment of postmeiotic gametes with ENU.

High-frequency induction of chromosomal rearrangements in mouse germ cells by the chemotherapeutic agent chlorambucil.

Recent mutagenesis studies have demonstrated that the chemotherapeutic agent, chlorambucil (CHL), is highly mutagenic in male germ cells of the mouse. Post-meiotic germ cells, and especially early spermatids, are the most sensitive to the cytotoxic and mutagenic effects of this agent. Genetic, cytogenetic and molecular analyses of many induced mutations have shown that, in these germ-cell stages, CHL induces predominantly chromosomal rearrangements (deletions and translocations), and mutation-rate studies show that, in terms of tolerated doses, CHL is perhaps five to ten times more efficient in inducing rearrangements than is radiation exposure. Appropriate breeding protocols, along with knowledge of the advantages and limitations associated with the use of CHL, can be used to expand the current resource of chromosomal rearrangements in the mouse and to provide new phenotype-associated mutations amenable to positional-cloning techniques. The analysis of CHL-induced mutations has also contributed to understanding the factors that affect the yield and nature of chemically induced germline mutations in mammals.

Isolation of temperature-sensitive mouse FM3A cell mutants exhibiting conditional chromosomal instability.

Fourteen mutants exhibiting conditional induction of sister chromatid exchanges (SCEs) and/or chromosomal aberrations (CAs) were selected out of 65 temperature-sensitive (for growth) mutants from mouse FM3A cells treated with N-methyl-N'-nitro-N-nitrosoguanidine. The mutants with chromosomal abnormality at the nonpermissive temperature were classified into three groups. The group 1 mutant manifested mainly SCEs at the nonpermissive temperature. The group 2 mutants manifested both SCEs and CAs. The group 3 mutants, including ts-131b, a mutant defective in DNA replication and previously described, manifested only CAs. A substantial number of SCEs accompanied by CAs at the site of SCEs were observed in some of the group 2 mutants at the nonpermissive temperature. The results suggest that there are at least three processes involved in the formation of SCEs and CAs, one is common to both phenomena while the others are independent. Some other mutants belonging to the groups 1 and 2 displayed a high incidence of interchromosomal chromatid exchanges at the nonpermissive temperature, suggesting that the same genetic defects leading to high induction of SCEs correlate with induction of chromosomal rearrangements. From these results, the group 2 mutants were subdivided further into five classes, and the mutants in each class had different cytogenetic properties from one another. This indicates defects in at least several genes that participate in the production of SCEs or CAs. The mutants described should be useful for analyzing the mechanisms of SCE or CA formation, and also the mechanism of chromosomal rearrangements.

Effects of unequally fractionated X-ray exposures on the induction of chromosomal rearrangements in mouse spermatogonia

The induction of reciprocal translocations in mouse stem-cell spermatogonia was determined following different unequally fractionated X-ray exposures with 24 h between the fractions. The results indicate that quite variable levels of chromosomal damage can be induced using the same exposure schemes. This variation does not seem to be correlated with radiation set-up or mouse strain. In general, with higher conditioning exposures from 12.5 to 300 rad (or R), higher frequencies of translocations were produced using a larger second challenging exposure of 700–900 rad (or R). The increase in yields of aberrations was more or less paralleled by a shift from a strong deviation from a Poisson fit of the number of translocations per spermatocyte, to a good fit, suggesting a transition from the original heterogeneity of the stem cell population to a radiation induced, more homogeneous stage. Earlier observations concerning a threshold dose for sensitization (van Buul and Léonard, Mutation Res., 70 (1980) 95–101) could not be confirmed.

Radiation induced semi-sterility for genetic control purposes in the onion fly Hylemya antiqua (Meigen)

The study of the radiobiological and cytogenetic aspects of induced semi-sterility for application in the genetic control of the onion fly Hylemya antiqua (Meigen) has been continued. Doses of 1.5 krad of X-rays or 0.25 krad of fast neutrons were applied to males and 1.0 krad of X-rays or 0.25 krad of fast neutrons to seven day-old females. On the basis of semi-sterility (between 60% and 30% egg hatch) in backcrosses to normal flies, eleven strains were suspected of carrying a chromosomal rearrangement. Seven had a reciprocal translocation and two from a 1.5 krad X-ray treatment showed complex rearrangements. In two strains no rearrangements were found. Two homozygous translocations are described. Combining data of earlier experiments with the new results we concluded that the irradiation of males with low doses, 0.5 krad of X-rays or 0.25 krad of fast neutrons, is suitable for the induction of chromosomal rearrangements. Strains carrying rearrangements from such low dose treatments will be further used for genetic control experiments on the onion fly.