1 / 30

Graham Moore

The chromosome pairing locus in wheat. Graham Moore. Prophase I. Pachytene. Diplotene. Diakinesis. Zygotene. Prophase II. Metaphase I. Metaphase II. Leptotene. Telophase II. Anaphase I. Anaphase II. Telophase I. Meiosis. Homologous chromosomes must recognise each other,

courtney
Download Presentation

Graham Moore

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. The chromosome pairing locus in wheat Graham Moore

  2. Prophase I Pachytene Diplotene Diakinesis Zygotene Prophase II Metaphase I Metaphase II Leptotene Telophase II Anaphase I Anaphase II Telophase I Meiosis Homologous chromosomes must recognise each other, pair correctly and recombine 1 Diploid cell Paired homologues align on plate Homologues are separated 4 Haploid cells Sister chromatids are separated Incorrect pairing leads to unbalanced gametes and infertility

  3. Ph1 locus homologues Prevents pairing of homoeologous chromosomes and unbalanced gametes homoeologues Hexaploid wheatTriticumaestivum2n = 6x =42 To be fertile, true homologues must pair at meiosis 1 2 3 4 5 6 7 a b c d A a b c d B a b c d D

  4. Ph1’s effect- is important agronomically Wild species of wheat carry important traits for disease resistance and salt, cold and drought tolerance Wheat-rye hybrid Ph1 locus suppresses pairing between related chromosomes (homoeologous pairing) Ph1+ If Ph1 locus is deleted, pairing is induced between related chromosomes Ph1- **Strategic Goal** Can we from understanding Ph1 locus, switch Ph1 on and off in elite wheat varieties crossed with wild species?

  5. What is Ph1? Cloning - the issues • No natural variation in Ph1 phenotype -Can’t create segregating populations, the starting point of all previous positional cloning projects • EMS treatments don’t yield mutants • But X-Ray and fast neutron irradiation do -A single deletion (ph1b) of the locus = 70Mb in size • “Ph1 locus” arose on polyploidisation • The wheat genome is very large

  6. Defining the Ph1 locus Griffiths et al 2006 Al-Kaff et al 2008 Rice Deletions Deletions Deletions Wheat Brachypodium

  7. Cluster of Cyclin dependent kinase-like (Cdks) genes Rice All defective genes = Ph1 locus Large segment of Heterochromatin inserted on polyploidisation Wheat Hypothesis- the defective 5B Cdk copies are suppressing the activity of the related Cdks elsewhere in the genome. But how to take the study further in wheat?

  8. Ph1Cdk-like gene shows similarity to Cdk2 Cdk2 in mammals affects histone H1 phosphorylation So as a defective locus, does Ph1 suppress Cdk activity, hence Histone H1 phosphorylation?? Ph1 cdk+cyclinA compared to Cdk2+cyclinA Ph1-cdk gene Cdk2 Protein modelling Yousafzai and Al-kaff, 2010

  9. Does Ph1 affect histone HI phosphorylation? Cdk2 phosphorylates human histone H1 at: Human Histone H1 phosphorylationsites Consensus motifs (S/T) –P-X-K TPVK TPKK TPKK SPKK SPAK _ Is wheat histone H1 phosphorylated at Cdk2 consensus sites and is their phosphorylation altered by Ph1 ???

  10. Wheat HistoneH1 phosphorylated at Cdk2-type consensus (S/T) –P-X-K sites Cdk2-type phosphorylation on histone H1 is increased when Ph1 locus deleted Azahara Martinez, Ali Pendle, Alex Jones, Isabelle Colas

  11. Reduced homologous Pairing-univalents Homoeologous Pairing- 0 Ph1 copies Mutate or over-express Arabidopsis Cdk Reduced homologous Pairing-univalents Mutivalents increased Cdk activity 2 Ph1 copies Homologous pairing Bivalents Homologous pairing 6 Ph1 copies Reduced Homologous pairing- univalents reduced Cdk activity Reduced homologous pairing-univalents Greer et al 2012 Moshe Feldman 1966 John Doonan Metaphase I pairing

  12. Deleting Ph1 increases Cdk activity- which increases histone H1 phosphorylation, And we have pairing between related chromosomes So key question Can we mimic the effect of deleting Ph1 by increasing histone H1 phosphorylation and hence Induce pairing between related chromosomes??

  13. Does increased Cdk-type activity induce pairing between related chromosomes? • Okadaicacid inhibits phosphatases • Okadaic acid increases Histone H1 kinase activity • Does Okadaic acid induce pairing between related chromosomes? Detached tiller method

  14. Okadaic acid induces pairing of related chromosomes in a wheat x rye hybrid Okadaic acid - bivalents & other chromosomes associations No okadaic acid – mostly univalents So, okadaic acid treatment produces a similar effect on chromosome pairing of related chromosomes as deleting Ph1 Wheat X Rye – Ph1 deleted Homoeologouspairing Knight et al., 2010

  15. Does Okadaic acid treatment affect the same Cdk2 consensus site as Ph1??? yes The “Ph1” Cdk2-type consensus site shows increased phosphorylation with Okadaic acid treatment Increased histone H1 phosphorylation leads to more “open” /decondensed chromatin? How does this affect pairing /recombination?

  16. Our detailed understanding of the genes involved in recombination has come from models: yeast, C elegans, Drosophila – Little is known about homologue recognition

  17. Ph1 effect in wheat- don’t want incorrect associations here Homologues present Leptotene Diakinesis Zygotene Metaphase I Pachytene Diplotene Holm, 1986, 1988 6chromosomes incorrectly paired during zygotene 6 chromosomes associating incorrectly resolved at pachytene 21 correct pairs at metaphase I Ph1+ 42 chromosomes Ph1- 14 incorrectly paired during zygotene 14 chromosomes associating incorrectly not resolved at pachytene 14 chromosomes as univalents or multivalents 14 correct pairs 42 chromosomes Homologue recognition altered by Ph1 Resolution of incorrect associations altered by Ph1 At both these stages condensation changes occur which would be affected by histone H1 phosphorylation

  18. Ph1 effect in wheathybrids want incorrect associations here No homologues Ph1+ Gillies 1987 1 pair at metaphase I Wheat-kotschyi 35 chromosomes <20% pairing 65% pairing Wheat-rye 28 chromosomes 1 pair at metaphase I 30% pairing only at zygotene 30% pairing Little change at pachytene Wang 1988, Wang and Holm 1988 Ph1- 14 pairs at metaphase I Wheat-kotschyi 35 chromosomes >50% pairing >90% pairing 60% pairing at pachytene 30% pairing only at zygotene Wheat-rye 28 chromosomes 7 pairs at metaphase I increase in incorrect associations in absence of Ph1 No increase in incorrect associations in absence of Ph1 Resolution of incorrect associations altered by Ph1

  19. Effect on recognition?? Lack of Ph1 induces more incorrect pairing between homoeologues Wheat Lack of Ph1 induces more incorrect pairing between homoeologues in the absence of homologues?? Wheat-kotschyi But Lack of Ph1 does not induce more incorrect pairing between the homoeologues in the absence of homologues?? Wheat-rye What is happening??

  20. What happens at the homologue recognition stage in wheat? homologues “Decondensation ‘Elongation” of chromatin Rye segment PilarPrieto et al 2004 Nat Cell Biol telomeres homologous segments telomeres The identical chromosomes zip up from their telomere regions This conformation change now reported in C elegans

  21. In wheat- chromosomes remodel in both the presence and absence of Ph1 but there is asynchronous chromatin remodelling in the absence of Ph1 correlating with more incorrect associations at homologue recognition stage Ph1- Interstitial segments- 15% of the wheat chromosome Telomeres Ph1+ Ph1+ Ph1+ Ph1+ PilarPrieto et al 2004 Nat Cell Biol

  22. Identical segments Segments elongatedSynchronously before clustering 100% pairing • Similar segments Segmentselongatedbut Not Synchronously 50% pairing • Distinctsegments Reduced/Delayed 15% pairing Decondensation of chromosome segments linked to presence of homologous chromosomes and affects pairing Isabelle Colas et al 2008 PNAS

  23. In wheat-rye hybrids-without Ph1 homoeologous wheat-rye chromosomes only trigger a partial conformation change Ph1+ Ph1- Some Pairing No Pairing hybrid- Ph1- homoeologues hybrid- Ph1+ homoeologues Diploid- homologues Partial change not sufficient to induce more incorrect associations Ph1- heterochromatin telomeres Pairing

  24. The processing of incorrect associations –ie associations between related chromosomes at pachytene Gillies 1987 Wang 1988, Wang and Holm 1988 Ph1+ 1 pair at metaphase I Wheat-kotschyi 35 chromosomes <20% pairing 65% pairing Wheat-rye 28 chromosomes 30% pairing 1 pair at metaphase I 30% pairing only at zygotene Little change at pachytene Ph1- 14 pairs at metaphase I Wheat-kotschyi 35 chromosomes >50% pairing >90% pairing At pachytene Pairing increases to 60% 30% pairing only at zygotene Wheat-rye 28 chromosomes 7 pairs at metaphase I Resolution of incorrect associations altered by Ph1 The maintenance of incorrect associations without Ph1 correlates with significant increase in pairing (synapsis)

  25. Diverged (related) chromosomes pair via pegging process Colas et al., PNAS 2008 Homologues with divergent segments Chromosome segments peg together forming a circular structure Chromosome segments remodel telomeres The altered chromatin with Ph1 affectsCondensation/ Decondensation change at Pachytene/ Diplotene Little Synaptic adjustment with Ph1 Synaptic adjustment Non-homologous pairing without Ph1 at pachytene/ diplotene No recombination Chromosomes resolve recombination

  26. Synaptic adjustment

  27. Finally enhances correct chromosome segregation through regulating centromere pairing Meiosis I Metaphase I Anaphase I Chiasmata Separase Cohesion lost in arms Cohesion Spindle force Chromosome segregation via the centromeres

  28. enhances correct chromosome segregation through regulating centromere pairing Finally Centromeres in many plants (wheat, Arabidopsis, brachypodium) pair independently from telomeres and the rest of the chromosomes Synapsis can be initiated at centromeres independently from the telomeres Ph1 increases the stringency of centromere pairing- thus the fidelity of segregation Centromeres telomeres Martinez-Perez et al., 2001 Nature

  29. Conclusions (Phosphorylation (Histone)hI alters chromatin and hence homologue recognition, synaptic adjustment and chromosome segregation during meiosis

  30. Thanks to… Genomics- Comparative-BAC library-mutants Tracie Draeger (Foote), Michael Roberts, Lijia Qu, Terry Miller, Steve Reader, Simon Griffiths, Sebastien Allouis, Rebecca Sharp, Kath Mortimer, Emilie Knight, Nadia Al-Kaff, Vera Thole, Ruoyu Wen Ph1 into other species-Brachypodium/Arabidopsis RuoyuWen, Vera Thole, Philippe Vain, John Doonan, Peter Shaw Protein modelling-FaridoonYousafzai, Nadia Al-Kaff Phosphoproteomics- advanced mass spec Azahara Martinez-Raminez, Ali Pendle, Isabelle Colas, Alex Jones, Peter Shaw Cell biology – 3-D visualisation- Luis Aragon, Fadri Martinez, PilarPrieto, Mike Wanous, Isabelle Colas, Emma Greer, Azahara Martinez-Raminez, Peter Shaw

More Related