Genetic flux in plants
The basis of my career as molecular biologist was laid by work on bacteriophages fd (in Tuebingen and Yale) and lambda (Biocenter, Basel). The studies of morphogenesis of lambda led to in vitro assembly and DNA packaging of this beautiful model virus. This was early times of recombinant DNA and the possibility to make recombinant lambda DNA infectious by packaging it into its preformed capsid was most welcome. As an extension of this work hybrid plasmids containing the phage packaging site cos, later called cosmids were developed. These allowed the cloning of large fragments of DNA and libraries of genomic DNA of many organisms were produced all over the world. However, the most interesting aspect is that of unintended, serendipitous findings applicable for unforeseen uses.
With the move from the Biocenter to the FMI came the move to eukaryotic organisms, specifically plants. In collaboration with plant scientists already located at the FMI studies on transformation of and genetic recombination in plants were conducted. Especially intriguing thereby was to get to know the prokaryotic organism Agrobacterium tumefaciens which has been shown a long time ago to be able to genetically transform (some) plants. The study of the mechanism of transfer of DNA to plants was a fascinating lesson. Again, the naïve and curiosity-driven search for basic principles led to the discovery of the agronomically important grasses such as maize as unforeseen hosts for the bacterium's DNA transfer.
Genomes change over time; an interesting and partially essential contribution to this change is homologous recombination, active as DNA repair pathway in somatic tissue and of critical importance for rearrangement of genes during meiosis. With the help of specially designed marker genes in the transformed model plant Arabidopsis thaliana somatic recombination events could be monitored. These plants allowed the isolation of mutant plants changed in one or the other aspect of the recombination pathway. Especially fascinating was the finding that not only agents acting directly on the DNA but also other environmentally important influences such as pathogen attack led to increases in homologous recombination. Could this be part of evolutionary drive? In a step further, plants treated with UV or a molecule imitating a pathogen provided their untreated progeny with a molecularly undefined, but certainly epigenetically based kind of "memory" of their experience; progeny of treated plants exhibited a higher level of homologous recombination than progeny of untreated plants.
I have been especially privileged to witness big steps in the understanding of the molecular basis of life such as cloning of DNA and later transformation of lower and higher eukaryotic organisms including plants. I am equally privileged for having been able to contribute.
Presently I am enjoying a multifaceted life. I am trying, using collaborations, to further explore the nature of the epigenetic changes mentioned above. I am trying to return the work others have done before to guarantee the infrastructure and quality of scientific institutions (Advisory Boards), to help in evaluations of granting agencies and scientific journals. In addition, I am a consultant of European and international networks. These, as well as the intellectually challenging scientific spirit of the FMI, the unbroken chain of invitations to interesting meetings and other activities keep me very busy.
Kovalchuk I, Kovalchuk O, Arkhipov A, Hohn B (1998) Transgenic plants are sensitive bioindicators of nuclear pollution caused by the Chernobyl accidentNature Biotechnol 16:1054-1059
Marvin DA, Hohn B (1969) Filamentous bacterial virusesBacteriol Rev 33:173
Ries G, Heller W, Puchta H, Sandermann H, Seidlitz HK, Hohn B (2000) Elevated UV-B radiation reduces genome stability in plantsNature 406:98-101
Hohn B, Hohn Th (1974) Activity of empty, headlike particles for packaging of lambda DNA in vitroProc Natl Acad Sci USA 71:2372
Hohn B, Murray K (1977) Packaging recombinant DNA molecules into bacteriophage particles, in vitroProc Natl Acad Sci USA 74:3259
Kovalchuk O, Dubrova Y, Arkhipov A, Hohn B, Kovalchuk I (2000) Wheat microsatellite mutation rate after the Chernobyl accidentNature 407:583-584
Georgopoulos C, Hohn B (1978) Identification of a host protein responsible for bacteriophage morphogenesis (gro E.)Proc Natl Acad Sci USA 75:131
Lucht J, Mauch-Mani B, Steiner H-Y, Metraux J-P, Ryals J, Hohn B (2002) Pathogen stress increases somatic recombination frequency in ArabidopsisNature Genet 30:311-314
Collins J, Hohn B (1978) Cosmids: type of plasmid gene cloning vector that is packageable in vitro in bacteriophage lambda headsProc Natl Acad Sci USA 75:4242
Kovalchuk I, Kovalchuk O, Kalck V, Boyko V, Filkowski J, Heinlein M, Hohn B (2003) Pathogen-induced systemic plant signal triggers DNA rearrangementsNature 423:760-762
Pelczar P, Kalck V, Gomez D, Hohn B (2004) Agrobacterium tumefaciens virulence proteins ViD2 and VirE2 mediate precise integration of synthetic T-DNA complexes in mammalian cellsEMBO Rep 5:632-637
Koukolikova-Nicola Z, Shillito RD, Hohn B, Wang K, Van Montagu M, Zambryski P (1985) Involvement of circular intermediates in the transfer of T-DNA from Agrobacterium tumefaciens to plant cellsNature 31:191-196
Grimsley N, Hohn T, Davies J, Hohn B (1987) Agrobacterium-mediated delivery of infectious maize streak virus into maize plantsNature 325:177-179
Fritsch O, Benvenuto G, Bowler C, Molinier J, Hohn B (2004) The INO80 protein controls homologous recombination in Arabidopsis thalianaMol Cell (in press)
Schuermann D, Molinier J, Fritsch O, Hohn B (2005) The dual nature of homologous recombination in plantsTrends Genet 21:172-181
Molinier J, Ries G, Zipfel C, Hohn B (2006) Transgenerational memory of stress in plantsNature 442:1046-1049
Bakkeren G, Koukolikova-Nicola K, Grimsley N, Hohn B (1989) Recovery of Agrobacterium tumefaciens T-DNA molecules from whole plants early after transferCell 57:847-857
Swoboda P, Gal S, Hohn B, Puchta H (1994) Intrachromosomal homologous recombination in whole plantsEMBO J 13:484-489
Schuermann D, Fritsch O, Lucht JM, Hohn B (2009) Replication stress leads to genome instabilities in Arabidopsis DNA polymerase (delta) mutantsPlant Cell 2009 Oct 2 [Epub ahead of print]