Alexander Knoll

Publications

• 4.27

  Impact points

  The role of DNA helicases and their interaction partners in genome stability and meiotic recombination in plants.

  Alexander Knoll, Holger Puchta

  Journal of experimental botany. 11/2010; 62(5):1565-79.

  DNA helicases are enzymes that are able to unwind DNA by the use of the energy-equivalent ATP. They play essential roles in DNA replication, DNA repair, and DNA recombination in all organisms. As homologous recombination occurs in somatic and meiotic cells, the same proteins may participate in both ... [more] DNA helicases are enzymes that are able to unwind DNA by the use of the energy-equivalent ATP. They play essential roles in DNA replication, DNA repair, and DNA recombination in all organisms. As homologous recombination occurs in somatic and meiotic cells, the same proteins may participate in both processes, albeit not necessarily with identical functions. DNA helicases involved in genome stability and meiotic recombination are the focus of this review. The role of these enzymes and their characterized interaction partners in plants will be summarized. Although most factors are conserved in eukaryotes, plant-specific features are becoming apparent. In the RecQ helicase family, Arabidopsis thaliana RECQ4A has been shown before to be the functional homologue of the well-researched baker's yeast Sgs1 and human BLM proteins. It was surprising to find that its interaction partners AtRMI1 and AtTOP3α are absolutely essential for meiotic recombination in plants, where they are central factors of a formerly underappreciated dissolution step of recombination intermediates. In the expanding group of anti-recombinases, future analysis of plant helicases is especially promising. While no FBH1 homologue is present, the Arabidopsis genome contains homologues of both SRS2 and RTEL1. Yeast and mammals, on the other hand. only possess homologues of either one or the other of these helicases. Plants also contain several other classes of helicases that are known from other organisms to be involved in the preservation of genome stability: FANCM is conserved with parts of the human Fanconi anaemia proteins, as are homologues of the Swi2/Snf2 family and of PIF1.
• 9.53

  Impact points

  Topoisomerase 3alpha and RMI1 Suppress Somatic Crossovers and Are Essential for Resolution of Meiotic Recombination Intermediates in Arabidopsis thaliana.

  Frank Hartung, Stefanie Suer, Alexander Knoll, Rebecca Wurz-Wildersinn, Holger Puchta

  PLoS genetics. 01/2009; 4(12):e1000285.

  Topoisomerases are enzymes with crucial functions in DNA metabolism. They are ubiquitously present in prokaryotes and eukaryotes and modify the steady-state level of DNA supercoiling. Biochemical analyses indicate that Topoisomerase 3alpha (TOP3alpha) functions together with a RecQ DNA helicase and ... [more] Topoisomerases are enzymes with crucial functions in DNA metabolism. They are ubiquitously present in prokaryotes and eukaryotes and modify the steady-state level of DNA supercoiling. Biochemical analyses indicate that Topoisomerase 3alpha (TOP3alpha) functions together with a RecQ DNA helicase and a third partner, RMI1/BLAP75, in the resolution step of homologous recombination in a process called Holliday Junction dissolution in eukaryotes. Apart from that, little is known about the role of TOP3alpha in higher eukaryotes, as knockout mutants show early lethality or strong developmental defects. Using a hypomorphic insertion mutant of Arabidopsis thaliana (top3alpha-2), which is viable but completely sterile, we were able to define three different functions of the protein in mitosis and meiosis. The top3alpha-2 line exhibits fragmented chromosomes during mitosis and sensitivity to camptothecin, suggesting an important role in chromosome segregation partly overlapping with that of type IB topoisomerases. Furthermore, AtTOP3alpha, together with AtRECQ4A and AtRMI1, is involved in the suppression of crossover recombination in somatic cells as well as DNA repair in both mammals and A. thaliana. Surprisingly, AtTOP3alpha is also essential for meiosis. The phenotype of chromosome fragmentation, bridges, and telophase I arrest can be suppressed by AtSPO11 and AtRAD51 mutations, indicating that the protein is required for the resolution of recombination intermediates. As Atrmi1 mutants have a similar meiotic phenotype to Attop3alpha mutants, both proteins seem to be involved in a mechanism safeguarding the entangling of homologous chromosomes during meiosis. The requirement of AtTOP3alpha and AtRMI1 in a late step of meiotic recombination strongly hints at the possibility that the dissolution of double Holliday Junctions via a hemicatenane intermediate is indeed an indispensable step of meiotic recombination.

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• Identification, isolation and characterization of a cc-Nbs-Lrr candidate disease resistance gene family in grapevine

  Andreas Kortekamp, Leocir Welter, Sarah Vogt, Alexander Knoll, Florian Schwander, Reinhard Töpfer, Eva Zyprian

  Molecular Breeding. 01/2008; 22:421-432.

• Topoisomerase 3A and RMI1 suppress somatic crossovers and are essential for resolution of meiotic recombination intermediates in Arabidopsis thaliana

  F Hartung, S. Suer, A. Knoll, R. Wurz-Wildersinn, H Puchta

• Role of Human Disease Genes for the Maintenance of Genome Stability in Plants

  H Puchta, D. Kobbe, K. Wanieck, A. Knoll, S. Suer, M. Focke, F Hartung