Inheritance in F1 and transgressive variability in F2 of the main ear length by crossing wheat varieties with different maturity

In 2017–2019, the nature of the inheritance of ear length in F1 and transgressive variability in F2 populations obtained by hybridization of soft winter wheat varieties with different maturity were studied. It was found that in most combinations of crossbreeding, inheritance of ear length had a positive overdominance (hp = 1.1–39.0). A positive hypothetical heterosis was determined in early-maturing varieties in the maternal form, with the exception of the Kolchuga / Chornyava combination, by the length of the main ear (Ht = 3.6–44.8 %). a positive true heterosis (Hbt=1,1–32.9 %) was found in 15 of 20 hybrids. During the hybridization of medium-early, medium-ripe and medium-late varieties, all hybrids showed a positive hypothetical heterosis and 19 of 22 combinations had positive true heterosis. A significant influence of hybridization components on the indicators of the phenotypic dominance degree, hypothetical and true heterosis was established. Most of the F2 populations significantly exceeded the parental components of hybridization by the extreme maximum indexes of the main ear length, which indicates a significant shaping process and the possibility of selection on the basis of the studied trait. The maximum length of the main ear (10.3–12.1) was formed by most populations in which the maternal forms were varieties Kolchuga and Chornyava, as well as combinations Zolotokolos / Chornyava, Zolotokolosa / Stolychna and Yednist / Vidrada. The extreme maximum values reached 13.0–15.0 cm. In 36 of the 42 F2 populations, a positive degree and frequency of transgressions by the length of the main ear were determined, and their indexes largely depended on the pairs selection for hybridization. The highest degree of positive transgression was observed in the population Yednist / Vidrada (44.4 %) with a recombinant frequency of 86.7 %. Populations were characterized by a high degree and frequency of positive transgressions: Kolchuga / Yednist; Myronivska early / Antonivka; Myronivska early / Vdala; Zolotokolosa / Vidrada; Dobirna / Pyvna; Zolotokolosa / Stolychna; Zolotokolosa / Shchedra nyva; Myronivska early / Yednist; Myronivska early / Zolotokolosa; Myronivska early / B.Ts. n / a. Key words: soft winter wheat, maturity of varieties, combinations of crossbreeding, inheritance, hybrids, ear length, hypothetical and true heterosis, degree of phenotypic dominance, F2 populations, degree and frequency of transgressions.

Homoeologous Recombination: A Novel and Efficient System for Broadening the Genetic Variability in Wheat

Gene transfer from wild wheat relatives to bread wheat is restricted to homologous recombination. The presence of the Pairing homoeologous 1 (Ph1) gene in the long arm of wheat chromosome 5B allows only homologous chromosomes to pair and recombine, resulting in diploid inheritance of polyploid wheat. Previously, we identified a potent homoeologous pairing promotor gene(s) (Hpp-5Mg); its carrier chromosome 5Mg derived from Aegilops geniculata and its wheat homoeologous chromosome 5D freely recombined in the presence of the Ph1 gene. In this study, we investigated the effect of Hpp-5Mg on homoeologous recombination in the absence of Ph1. In Hpp-5Mg/ph1bph1b plants, we observed a vast genome-wide increase in homoeologous recombination and multiple crossovers (CO), including CO breakpoints in proximal regions of the chromosomes where recombination is known to be suppressed. We tested the efficacy of Hpp-5Mg/ph1bph1b-induced homoeologous recombination by producing new recombinants for the wheat streak mosaic virus resistance gene, Wsm3, present in the wheat-Thinopyrum intermedium Robertsonian translocation (RobT T7BS.7S#3L). A recombination frequency of 6.5% was detected by screening the progenies double monosomic for T7BS.7S#3L and 7B by genomic in situ hybridization. This recombination frequency was about 100-fold higher compared with the recombinant frequency of 0.06% observed by using ph1b-induced homoeologous recombination alone. Our results indicate that chromosome 5Mg promotes homoeologous recombination between wheat and wild wheat relative chromosomes, which helps in the generation of pre-breeding materials thereby accelerating wheat crop improvement.

Conjugational Genetic Exchange in the Hyperthermophilic Archaeon Sulfolobus acidocaldarius: Intragenic Recombination with Minimal Dependence on Marker Separation

ABSTRACT In Sulfolobus acidocaldarius conjugation assays, recombinant frequency was relatively constant for marker separations from 1,154 bp down to about 50 bp and readily detectable at 10 bp. Three-factor crosses revealed little, if any, genetic linkage over distances of 500 to 600 bp, and large deletion mutants were good donors but poor recipients in matings. The results indicate that most intragenic recombination events occur at one of the mutations, not in the interval between them.

UV Irradiation Causes the Loss of Viable Mitotic Recombinants in Schizosaccharomyces pombe Cells Lacking the G2/M DNA Damage Checkpoint

Elevated mitotic recombination and cell cycle delays are two of the cellular responses to UV-induced DNA damage. Cell cycle delays in response to DNA damage are mediated via checkpoint proteins. Two distinct DNA damage checkpoints have been characterized in Schizosaccharomyces pombe: an intra-S-phase checkpoint slows replication and a G2/M checkpoint stops cells passing from G2 into mitosis. In this study we have sought to determine whether UV damage-induced mitotic intrachromosomal recombination relies on damage-induced cell cycle delays. The spontaneous and UV-induced recombination phenotypes were determined for checkpoint mutants lacking the intra-S and/or the G2/M checkpoint. Spontaneous mitotic recombinants are thought to arise due to endogenous DNA damage and/or intrinsic stalling of replication forks. Cells lacking only the intra-S checkpoint exhibited no UV-induced increase in the frequency of recombinants above spontaneous levels. Mutants lacking the G2/M checkpoint exhibited a novel phenotype; following UV irradiation the recombinant frequency fell below the frequency of spontaneous recombinants. This implies that, as well as UV-induced recombinants, spontaneous recombinants are also lost in G2/M mutants after UV irradiation. Therefore, as well as lack of time for DNA repair, loss of spontaneous and damage-induced recombinants also contributes to cell death in UV-irradiated G2/M checkpoint mutants.

Tomato chromosome 6: effect of alien chromosomal segments on recombinant frequencies

Variation in recombinant frequencies at two adjacent intervals on chromosome 6 of tomato (Lycopersicon esculentum Mill.) has been studied in seven lines that differ in the amount and origin of introgressed segments from wild species. These lines were all crossed to a genotype homozygous recessive for the markers tl, yv, and c, which define the centromere spanning region tl–yv and the long arm region yv–c. Recombinants were identified in large F2, populations consisting of over 30 000 plants in total. Application of molecular markers provided additional information on the distribution of crossover events within the centromere-containing interval tl–yv. A decrease in recombination at the marked intervals correlated with the presence of an alien segment. Suppression of recombination was up to sixfold in the centromere spanning interval tl–yv depending on the source and size of the introgression, and was restricted to the alien segments with no strong effect on the neighbouring intervals. Key words : recombinant frequency, Lycopersicon esculentum, morphological markers, introgressions, centromere.

HOMOLOGOUS RECOMBINATION IN ESCHERICHIA COLI: DEPENDENCE ON SUBSTRATE LENGTH AND HOMOLOGY

ABSTRACT We studied the in vivo recombination between homologous DNA sequences cloned in phage lambda and a pBR322-derived plasmid by assaying for the formation of phage-plasmid cointegrates by a single (or an odd number of) reciprocal exchange. (1) Recombination proceeds by the RecBC pathway in wild-type cells and by low levels of a RecF-dependent pathway in recBC - cells. The RecE pathway appears not to generate phage-plasmid cointegrates. (2) Recombination is linearly dependent on the length of the homologous sequences. In both RecBC and RecF-dependent pathways there is a minimal length, called the minimal efficient processing segment (MEPS), below which recombination becomes inefficient. The length of MEPS is between 23-27 base pairs (bp) and between 44-90 bp for the RecBC- and RecF-dependent pathways, respectively. A model, based on overlapping MEPS, of the correlation of genetic length with physical length is presented. The bases for the different MEPS length of the two pathways are discussed in relationship to the enzymes specific to each pathway. (3) The RecBC and the RecF-dependent pathways are each very sensitive to substrate homology. In wild-type E. coli, reduction of homology from 100% to 90% decreases recombinant frequency over 40-fold. The homology dependence of the RecBC and RecF-dependent pathways are similar. This suggests that a component common to both, probably recA, is responsible for the recognition of homology.

INVOLVEMENT OF GENE 49 IN RECOMBINATION OF BACTERIOPHAGE T4

ABSTRACT The role of T4 gene 49 in recombination was investigated using its conditional-lethal amber (am) and temperature-sensitive (ts) mutants. When measured in genetic tests, defects in gene 49 produced a recombination-deficient phenotype. However, DNA synthesized in cells infected with a ts mutant (tsC9) at a nonpermissive temperature appeared to be in a recombinogenic state: after restitution of gene function by shifting to a permissive temperature, the recombinant frequency among progeny increased rapidly even when DNA replication was blocked by an inhibitor. Growth of a gene 49-defective mutant was suppressed by an additional mutation in gene uvs X, but recombination between rII markers was not.

MAPABILITY OF VERY CLOSE MARKERS OF BACTERIOPHAGE Λ

ABSTRACT Recombinant frequency was compared with nucleotide distance in crosses involving markers in either the P RM or the cy region of phage λ. For each pair of markers, we performed reciprocal four-factor crosses of the following types: (I) A + m 1 + m 2 - B - × A - m 1 - m 2 + B +; and (II) A + m 1 - m 2 + B - × A - m 1 + m 2 - B +. In crosses of type I, the frequency of A + m 1 + m 2 + B + recombinants among total (selected) A + B + progeny was directly proportional to nucleotide distance between m 1 and m 2 in the range from 3 to 160 nucleotides. When less than three nucleotides separated m 1 and m 2, the measured yields of m 1 + m 2 + recombinants were significantly depressed.