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Trude Schwarzacher: #ECA2015 European Cytogenetics Conference plenary talk:150 years since Mendel's laws of heredity

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Trude Schwarzacher Plenary talk at European Cytogenetics Conference, Strasbourg, July 2015, to commemorate 150 years since publication of Gregor Mendel's work on the laws of genetic inheritance in 1865. This was two decades before chromosomes were described.

2015 marks the 150th anniversary of the presentation and publication of Mendel’s seminal paper presenting his Laws of Heredity. One expects that the unexciting and uninformative title Versuche über Pflanzenhybriden (Studies of plant hybrids) in his paper was one reason it was ignored – the importance of a paper title for finding work is something we have discussed here on AoBBlog and regularly among Annals of Botany Editors! In the Slideshare talk, Trude Schwarzacher discussed research in Mendel’s time, when ‘blended inheritance’ was accepted, and then how Mendel came to carry out the work. Not least, he was taught by the physicist Christian Doppler at the University of Vienna, no doubt implanting the centrality of numeracy and what we now consider statistics, to understanding all phenomena, including those of biology.

Trude also points out that of the seven characters Mendel worked with in pea, two are still very relevant to breeding of modern crops: the terminal flowering character, and dwarfism of the whole plant. The synthesis of the results in Mendel’s original paper, even today, is remarkable with considerable interpretation and presentation of a general model of inheritance: I do wonder how many modern referees would quibble about "unsubstantiated extensions"? Trude discusses Mendel’s interactions with another important botanist of the time, Karl Wilhelm Naegeli of Munich; in some ways, though, this was unfortunate in that firstly, it is not clear how much Naegeli understood the significance of Mendel’s genetical results and the laws of heredity, and also had the suggestion to work with the hawkweeds, genus Hieraceum, which includes many polyploids and apomicts. Hardly a model species to use to understand the principles of genetic inheritance, and no doubt disheartening for the Monk by then working in Brno! The final section of Trude’s talk puts Mendel’s work into the context of chromosomes, as might be expected in a cytogenetics conference, although cell division and chromosomes were not described until later in the 19th century – the slideshare embedded above shows some images from these early work, with more recent results from her own lab.

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Trude Schwarzacher: #ECA2015 European Cytogenetics Conference plenary talk:150 years since Mendel's laws of heredity

  1. 1. Mendel and his time in the light of cytogenetics Trude Schwarzacher University of Leicester Department of Genetics TS32@le.ac.uk Gregor Mendel (1822-1884) www.molcyt.com UserID/PW ‘visitor’
  2. 2. Hugo Iltis ‘Few publications have so enduringly and variously influenced science as had the short monograph [Versuche über Pflanzenhybriden] by the Augustinian monk of Brünn [now Brno], Pater Gregor Mendel. Forgotten for decades, within a few years after its rediscovery it gave a mighty impetus to the doctrine of heredity; and as Mendelism, his teaching had now become the central theme of biological research as well as the foundation of manifold practical application’ Mendel’s life (The Life of Mendel,1966)
  3. 3.  Mendel’s life  Mendel’s experiments  Why was he forgotten?  What was known about chromosomes at the time of Mendel?  Mendel’s rediscovery at 1900  How has chromosome biology developed since  Some examples from our own research related to Mendel and plant hybridization Overview
  4. 4. 20 July 1822: born as Johann Mendel, Heinzendorf bei Odrau, Austrian Empire (now Hynčice, Czech Republic) 1840 – 1843: practical and theoretical philosophy and physics at the University of Olomouc Mendel’s life
  5. 5. 1843: joined as Pater Gregor the Augustinian Monastery, Brünn (now Brno) 1847: ordained priest 1851-1853: Natural history at the University of Vienna under Franz Ungar (professor of plant physiology) and Christian Doppler (professor of physics) 1853 onwards: supply teacher at Brno; he failed the exam to become a certified teacher twice 1857-1864: Experiments with peas Spring 1865: presented the results and generalizations at two meetings of the Natural History Society of Brünn Mendel’s life
  6. 6. 1866: The papers were printed in the Proceedings of the Society distributed in Europe and America 1866: Mendel consults Karl Wilhelm Nägeli of Munich, leading botanist of the time. Nägeli does not understand the significance of Mendel’s results and laws of heredity 1868: Becomes abbot; and has decreasing time for scientific activities 1869: Results on Hieraceum 6 January 1884: died at the age of 61 Mendel’s life
  7. 7. Mendel Memorial in Brno Mendel’s life Pat Heslop-Harrison in 2001 Jack Heslop-Harrison in 1933
  8. 8.  Mendel’s life  Mendel’s experiments  Why was he forgotten?  What was known about chromosomes at the time of Mendel  Mendel’s rediscovery  How has chromosome biology developed since  Some examples from our own research Overview
  9. 9. But Mendel does not mean hybrids between two species, he means between two different types or variants “… the regularity with which the same hybrid forms resulted, every time fertilization between the same species occurred, gave the incentive to further controlled experiments.”
  10. 10. Experiments with peas Crossing (making hybrids with) varieties with clear and different characters or traits Drawing from many websites including http://guestblog.scientopia.org/2012/08/03/mud-sticks-especially-if-you- are-gregor-mendel/
  11. 11. Experiments with peas Law of segregation
  12. 12. Experiments with peas Law of independent assortment
  13. 13. Experiments with peas Defined the terms recessive and dominant Spoke of invisible ‘factors’ - now called genes – that were responsible for the visible traits
  14. 14. Genetic location of Mendel's seven characters on pea linkage groups. Yellow versus green cotyledons II/ii on linkage group (I); seed coat (and flower) colour AA/aa on linkage group (II); tall versus dwarf plants (LeLe/lele) on linkage group (III); difference in the form of the ripe pods (PP/pp or VV/vv) on linkage groups (III) and (VI), respectively; difference in the position of the flower (FasFas/fasfas or FaFa/fafa) on linkage groups (III) or(IV), respectively; round versus wrinkled (RR/rr) on linkage group (V); and colour of unripe pod (GpGp/gpgp) on linkage group (V). The types of lesion in Mendel's mutants are various: transposon insertion (r), missense mutation (le-1), splice variant (a) and amino acid insertion (i). Ellis et al. 2011: Mendel, 150 years on. Trends in Plant Science 11:590-596.
  15. 15. 2010, doi:10.1371/journal.pone.0013230
  16. 16. Conclusions/Significance:  Identification of the pea genes A that is the factor determining anthocyanin pigmentation in pea  The A gene encodes a bHLH transcription factor.  The white flowered mutant allele most likely used by Mendel is a simple G to A transition in a splice donor site that leads to a mis- spliced mRNA with a premature stop codon
  17. 17. The wrinkled-seed mutant (rr) of pea (Pisum sativum L.) arose through mutation of the gene encoding starch-branching enzyme isoform I (SBE1) by insertion of a transposon-like element into the coding sequence. Starch amount and amylopectin are reduced and as a consequence sucrose level is higher that causes increased uptake of water. When the seed tries the wrinkled phenotype results.
  18. 18.  Mendel’s life  Mendel’s experiments  Why was he forgotten?  What was known about chromosomes at the time of Mendel  Mendel’s rediscovery  How has chromosome biology developed since  Some examples from our own research Overview
  19. 19. Mendel’s experiments Mendel’s 1866 paper was cited only three times over the next thirty-five years.  Was Mendel ahead of his time?  Did he have bad luck?  Boring title and Mendel did not sell his theory well.  Mislead by Nägeli to work on Hieraceum that did not prove his theory  His paper was seen as essentially about hybridization rather than inheritance
  20. 20.  His paper was seen as essentially about hybridization rather than inheritance.  Blended inheritance was the accepted theory of inheritance where traits from each parent are averaged together.  not so different from what we now know to be the case for multiple genes and quantitative trait loci (QTL).  Mendelian discontinuous inheritance applies to single genes only. Inheritance
  21. 21.  Mendel’s life  Mendel’s experiments  Why was he forgotten?  What was known about chromosomes at the time of Mendel  Mendel’s rediscovery  How has chromosome biology developed since  Some examples from our own research Overview
  22. 22. micro.magnet.fsu.edu/primer/museum/hooke.html First microscope observed cells
  23. 23. Compound microscope The lens closest to the object, called the Objective, is used to enlarge and invert the object into a 'real' image. The lens closest to the eye called the Eyepiece or Ocular acts essentially as a simple magnifier, used to view the image formed by the objective. The simple magnifier is a converging lens placed in front of the eye that increases the size of the image formed by the retina. www.math.ubc.ca/.../lewis/project.html The compound microscope, in its simplest form is a system of two converging lenses used to look at very small objects at short distances. E. Leitz, Wetzlar, Germany, 1894
  24. 24. Modern microscope www.math.ubc.ca/.../lewis/project.html E. Leitz, Wetzlar, Germany, 1894 Axioimager
  25. 25. Recording chromosome images  Drawings  Photography (1950-1980s)  Black and white  Colour  Digital images (1990s, now)  CCD cameras www.usyd.edu.au/.../cmicrodesign.shtml http://www-unix.oit.umass.edu/~coreya/yashica/micadpt.jpg First photograph: 1826, Eastmann (1884): film as known today. Microphotography 1920/30.
  26. 26. Chromosomes Early 19th century Cells and nuclei simply pinched in half to divide Anton Schneider (1873) First scientist to describe clearly the process of mitosis and the involvement of the ‘chromatic nuclear figure’
  27. 27. Eduard Strassburger (1875) Gives clear and detailed descriptions of cell division in plants Walther Flemming (1879-1882) Describes ‘Mitosis’ in animal cells Discovers lampbrush chromosomes Balbiani (1880) Polytene chromosomes Chromosome
  28. 28. Flemming 1882
  29. 29. Continuity of chromosomes throughout cell division Flemming 1882
  30. 30. Orientation of chromosomes within interphase  Rabl (1885)  Rabl orientation Salamandra maculata
  31. 31. 1B/1R wheatWheat containing chromosome 1RS Schwarzacher et al. 1992
  32. 32. Metaphase I Telomere Centromeres Interphase Rye Schwarzacher 2000
  33. 33. Gregor Mendel (1865) Formulated his laws of heredity without the knowledge of chromosomes Wilhelm Waldeyer (1888) Introduces the term ‘chromosome’ Weismann (1887) Puts forward ‘chromosome theory of inheritance’ 1900: When Mendel was rediscovered, it became clear that the behaviour of chromosomes at cell division (mitosis and particular meiosis) was exactly what was needed to explain the distribution of hereditary factors Waldeyer
  34. 34. Who and how was he rediscovered Mendel’s laws were rediscovered independently within two months of each other in Spring of 1900 by Hugo de Vries and Carl Correns, and to some extend the Austrian Erich von Tschermak. Following their publications, Mendel’s results were replicated and genetic linkage formally described. Rediscovery
  35. 35.  Mendel’s life  Mendel’s experiments  Why was he forgotten?  What was known about chromosomes at the time of Mendel  Mendel’s rediscovery  How has chromosome biology developed since  Some examples from our own research Overview
  36. 36. Bateson (1916) Described the concept of the gene Feulgen and Rossenbock (1924) Demonstrated the presence of DNA in chromosomes by histochemical staining Watson and Crick (1953) Structure of DNA Early studies on chromosomes were in insects and plants Morgan and his students (Drosophila; linkage groups) Barbara McClintock (maize, transposable elements) Number of chromosomes in human was not established until 1956 (J. Tijo and A. Levan) Chromosomes, genes and DNA
  37. 37. Fluorescent in situ hybridization (FISH)
  38. 38. FISH 1985 onwards Beta vulgaris Propidium idode FITC Images from molcyt.com (upper row) and chrombios.com (lower row)
  39. 39. Wheat, Hieraceum and Petunia Polyploid and diploid hybrids Oil seed rape, Brassica napus Petunia hybrida P. axillaris Hieraceum Wheat trials
  40. 40. Triticale wheat x rye hybrid Schwarzacher et al 1989, 1992 Total genomic DNA labels chromosomes according to their genome origin 2n=6x=42 AABBRR Annals of Botany 64, 315-324 and Theoretical and Applied Genetics 84, 778-786.
  41. 41. Rye and the genus Thinopyrum, including wild goat grasses and wheat grasses, has proven an excellent source for disease and biotic stress resitance Schwarzacher 2000
  42. 42. Six populations of wheat lines that include an alien chromosome arm from Thinopyrum intermedium carrying WSMV resistance (Wsm-1 gene) Characterization of new sources of Wheat streak mosaic virus resistance WSMV resistant and susceptible lines in field trials Bob Graybosch, USDA-ARS, University of Nebraska, USA Wheat ‘Mace’: Journal of Plant Registrations 3(1): 51-56.doi: 10.3198/jpr2008.06.0345crc 4D T4DL*4Ai#2S DAPI Afa Thin all (blue) (green) (red)
  43. 43. Some lines also carry a Thin or rye fragment on chromosome 1B Th. intermedium DNA pSc119.2/CS13 Rye DNA dpTa1/Afa The whole 1RS arm correlates with WSMV resistance in the absence of 4D and when together with 4D enhances resistance Ali, Graybosch, Hein, Heslop-Harrison, and Schwarzacher 2015
  44. 44. Hieraceum • Genus Hieraceum • Hawkweed (German Habichtskraut) • Family Asteraceae (Compositae) • Closely related to Taraxacum (Dandelion) • Probably 1,000+ species • Classification notoriously difficult with a lot of minor geographical variation Most reproduce exclusively asexually by means of seeds that are genetically identical to their mother plant (apomixis or agamospermy) Rubar Salih, Richard Gornall and Pat Heslop- Harrison
  45. 45. Hieraceum Taxon Section Chr number Ploidy Identifier code Source H.amaurostictum Walter Scott & R.C.Palmer Alpestria 2n=36 4x Hama01 Semblister H.attenuatifolium P.D.Sell & C.West Alpestria 2n=36 4x Hatt02 Laxo Burn H.australis (Beeby)Pugsley Alpestria 2n=36 4x Haus03 Burrafirth area, Unst H.breve Beeby Alpestria 2n=36 4x Hbre04 Ronas Voe H.difficile P.D.Sell & C.West Alpestria 2n=36 4x Hdif05 Okraquoy H.dilectum P.D.Sell & C.West Alpestria 2n=36 4x Hdil06 Laxo H.gratum P.D.Sell & C.West Alpestria 2n=36 4x Hgra08 Burra Firth, Unst H.hethlandiae (F.Hanb.) Pugsley Alpestria 2n=36 4x Hhet09 Mavis Grind H.northroense Pugsley Alpestria 2n=27 3x Hnor11 Burravoe, North Roe H.pugsleyi P.D.Sell & C.West Alpestria 2n=36 4x Hpug12 Whale Firth, Yell H.spenceanum Qalter Scott & R.C.Plamer Alpestria 2n=36 4x Hspe14 Sandness H.subtruncatum Beeby Alpestria 2n=36 4x Hsubt16 Scarvister, West Mainland H.vinicaule P.D.Sell & C.West Alpestria 2n=27 3x Hvin17 Whale Firth H.zetlandicum Beeby Alpestria 2n=36 4x Hzet18 Isbister, North Roe H.scottii P.D.Sell Oreadea 2n=36 4x Hsco13 Near Windy Scord H.subscoticum P.D.Sell Oreadea 2n=27 3x Hsubs15 Ronas Voe H.gothicoides Pugsley Tridentata 2n=37 4x Hgot07 Lunning H.lissolepium Roffey Tridentata 2n=36 4x Hlis10 Eric’s Ham, Yell H.umbellatum _ 2n=18 2x Humbi19 Sw/71.50 Samples supplied by Richard Gornall, Botanic Garden, University Leicester
  46. 46. HieraceumBarcoding Chloroplast Matk geneITS of the 45S rDNA Rubar Salih, Richard Gornall and Pat Heslop-Harrison
  47. 47. H. vinicaule H17 (2n=3x= 27) Genomic in situ hybridization with Hieracium umbellatum DNA H. northroense H11 (2n=3x= 27) Rubar Salih and Pat Heslop-Harrison 2014
  48. 48. FISH with rDNA probes 3x species have 3 or 6 sites 4x species have 4 or 8 sites H. vinicaule H17 (2n=3x= 27) H. amaurostictum H1 (2n=4x= 36) 45S rDNA 45S rDNA 5S rDNA Rubar Salih and Pat Heslop-Harrison 2014
  49. 49. K. Richert Poeggeler and Schwarzacher Diploid hybrid 2n=14 Petunia is a model for DNA transposon work P. hybrida Petunia inflata X P. axillaris 2n=14 x 2n=14
  50. 50. 1. Transposon insertion, blocks the colour production in the floral pigment pathway 2. Spontaneous excision of elements restores colour and causes variegation Extremely active endogenous dTph1 transposon system Gerats, A.G., Huits, H., Vrijlandt, E., Marana, C., Souer, E., and Beld, M. (1990). Molecular characterization of a nonautonomous transposable element (dTph1) of petunia. Plant Cell 2, 1121-1128. http://solgenomics.net/community/feature/200601.pl
  51. 51. Petunia Leader Cris Kuhlemeier with Quattrocchio, Sims, Mueller, Schranz, Bombarely,Richert-Pöggeler, Schwarzacher, Heslop-Harrison et al. P. inflata P. hybrida P.axillaris http://flower.ens-lyon.fr/PetuniaPlatform/Petunia_as_a_model.html
  52. 52. Solanaceae phylogeny Tomato Potato Tobacco Eric Schranz and Trude Schwarzacher 2015 adapted from Sarkinen, T., Bohs, L., Olmstead, R.G., and Knapp, S. (2013). A phylogenetic framework for evolutionary study of the nightshades (Solanaceae): a dated 1000-tip tree. BMC evolutionary biology 13, 214.
  53. 53. Repetitive DNA component in Petunia Petunia Consortium 2015
  54. 54. Organelle sequences from chloroplasts or mitochondria Sequences from viruses, Agrobacterium or other vectors Transgenes introduced with molecular biology methods Genes, regulatory and non- coding single copy sequences Dispersed repeats: Transposable Elements Repetitive DNA sequences Plant Nuclear Genome Tandem repeats DNA transposons copied and moved via DNA Retrotransposons amplifying via an RNA intermediate Centromeric repeats Structural components of chromosomes Telomeric repeats Simple sequence repeats or microsatellites Repeated genes Subtelomeric repeats 45S and 5S rRNA genes Blocks of tandem repeats at discrete chromosomal loci DNA sequence components of the plant nuclear genome Heslop-Harrison & Schmidt 2012. Encyclopedia of Life Sciences Other genes Horizontal DNA transfer
  55. 55. Petunia Vein Clearing Virus (PVCV, 7206bp) Richert-Poeggeler and Shepherd 1997 Virology 236, 137-146 Para-retrovirus Does not need genomic integration for replication
  56. 56. PVCV ePVCV metaviridae-like sequencesPVCV integrase +2 pol +3 gag-pol +2 l clone3 (8 kb) +2 metaviridae-like sequences PVCV (nt 665-6153) +3gag-pol -1 +1 l clone 4 (11.4 kb) K. Richert Poeggeler, J. Baily and Schwarzacher Metaviridae PVCV: Petunia vein clearing virus ePVCV are present and are clustered with Ty3-gypsy-like sequences Richert-Pöggeler, K.R., Noreen, F., Schwarzacher, T., Harper, G. and Hohn, T. (2003) Induction of infectious Petunia vein clearing (pararetro) virus from endogenous provirus in petunia. EMBO Journal 22: 4836-4845
  57. 57. PVCV K. Richert Poeggeler and Schwarzacher 2000YA
  58. 58. methylated DNA unmethylated DNA non-activatable copies (regulatory) siRNAs (21-25 nt) Low level transcripts PTGS non-activatable copies (silent ) activatable copies (potentially infectious) Defense against episomal virus Defense against episomal virus Epigenetic modifications viral suppressor? terminal redundant transcripts Transcript level sufficient for activation and suppressor production Epigenetic modifications Epigenetic modifications TGS more transcripts Weakening of epigenetic control Virus replication Cell-to-cell spread Symptoms of infection Staginnus C, Richert-Pöggeler KR (2006). Endogenous pararetroviruses: two-faced travelers in the plant genome. Trends Plant Sci 11: 485-491. PVCV may be induced by applying abiotic stress, leading to the development of viral symptoms and increased transcript and siRNA levels.
  59. 59. Molecular cytogenetics lab Niaz Ali Pat Heslop- Harrisonts32 @le.ac.uk www.molcyt.com UserID/PW ‘visitor’ @Pathh1 Rubar Salih Katja Richert- Poeggeler Richard Gornall
  60. 60. Thomas Cremer From cell theory to chromosome theory Scientific realization and theory alterations in early cell and heredity research 1985
  61. 61.  Mendel’s life  Mendel’s experiments  Why was he forgotten?  What was known about chromosomes at the time of Mendel  Mendel’s rediscovery  How has chromosome biology developed since  Some examples from our own research Overview
  62. 62. 150th anniversary Versuche über Pflanzenhybriden (Experiments with plant hybrids) 1865 Gregor Mendel (1822-1884)

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