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The plant breeders’ desire to control crossovers

Crossing over during meiosis. ×. Homologous chromosomes. Recombinant chromatids. Chiasma. P 1. P 2. ×. WW. RR. F 1. F 1. RW. The plant breeders’ desire to control crossovers. The success of a breeding program depends on the ability of plant breeders to bring the desired

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The plant breeders’ desire to control crossovers

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  1. Crossing over during meiosis × Homologous chromosomes Recombinant chromatids Chiasma P1 P2 × WW RR F1 F1 RW The plant breeders’ desire to control crossovers • The success of a breeding program depends on • the ability of plant breeders to bring the desired • alleles together in one hybrid. incomplete dominance • Meiotic recombination has a pivotal role in • successful plant breeding. • two factors determine recombination: • the number of chromosomes • the number and positions of crossovers

  2. Molecular marker systems InDel: Insertion-deletion SNP: Single nucleotide polymorphism SSLP: Simple sequence length polymorphism CAPS: Cleaved amplified polymorphic sequence Lukowitz et al., 2000

  3. F11 2 3 4 5 6 7 8 9 10 Col Ler F2 A B C D M E F v Ler Col Col Ler Col Ler Col Ler Ler Col Col Ler B D A F C E Ler/Total 50% 35% 25% 10% 15% 30% Molecular markers commonly used for mapping crossover frequency

  4. Arabidopsis and qrt 1mutants pollen development PMC: pollen mother cell Kirk E. Francis et al.,2006 Tetrad analysis • Tetrad analysis is a method for investigating genetic mechanisms based upon the analysis of all four • products of meiosis. • Tetrad analysis is useful for examining meiotic recombination and it has the flexibility to provide • insight into many aspects of inheritance. Gregory P. Copenhaver et al., 2000

  5. Fluorescent tetrad analysis in A. thaliana Construct a genome-wide library (single-insertion fluorescent-tagged lines) Cross to mutant lines with three different markers Pollen from plants that are heterozygous Detect differences in interference between wild-type and mutant plants

  6. Controlling crossover incidence • Internal factors: • genetic background, morphological and developmental differences, • Barley: 30% differences;Arabidopsis: 17% differences • Arabidopsis: secondary or tertiary branches have up to 16% more crossovers than primary branches • external factors: • environmental influences • lima bean: twofold difference (random environmental variation) • Arabidopsis: 18% differences (higher temperature) • Allium ursinum :decreased recombination frequencies (higher temperature) • Barley, rye: less susceptible to environmental influence • 2.chemical treatments or physical stress: • Hordeum : threefold increase by actinomycin D and diepoxubytane treatment • Arabidopsis :fourfold increase by heat shock • threefold increase by UV radiation • many proteins involved in crossover formation • In the Arabidopsis X-ray sensitive4 mutant recombination frequency increased over twofold. • In the tomato overexpression of MLH1, led to a 10% increase in chiasma frequency. • In the Arabidopsis twofold increase of recombination frequency upon overexpression of RAD51 MutL homolog1 (MLH1): which encodes a mismatch repair protein Radiation sensitive 51 (RAD51): a gene involved in DNA repair

  7. Crossovers follow changes in chromosome structure Less frequent in pericentromere areas Tandem repeats in distal heterochromatin blocks in A. fistulosum Short terminal deletion in the pairing chromosomes can reduce crossover formation. But up to sevenfold increase of crossovers on the long arm of that same chromosome. Crossover frequencies increased in adjacent homologous sequences

  8. Crossovers in homoeologous regions P1 P2 × Introgressive hybridization P2 Recurrent backcrosses × Integrate valuable traits Imperative to find the mechanisms and genes Introgressed segment Homoeologous counterpart control the pairing between homoeologous segments Recurrent backcrosses Genes ,that influence homoeologous recombination: Ph1 : inhibits homoeologous pairing. In the absence of Ph1, pairing and recombination between homoeologous chromosomes is frequent. PrBn, comparable function with Ph1. MSH2or MSH3: encode mismatch repair proteins might promote homoeologous recombination . Crossover

  9. Preserving elite genotypes selected homozygous parents P1 P2 × F1 F1 hybrids bred unique combination of alleles and outperform their parents. Reverse breeding : a method for efficiently producing homozygous plants from a heterozygous starting plant.

  10. Conclusions On the one hand, expect a revival of classic meiotic research: variability within crops, within the plants or induced by internal and external factors might be evaluated using high-throughput marker technology. On the other hand, foresee that an increasing knowledge on the molecular control of meiosis might create new applications for plant breeding

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