title: Enhanced homologous recombination caused by the non-transcribed spacer of the rDNA in Arabidopsis.
abstract: The problem of the low frequency of homologous recombination observed in higher plants has been approached in several ways. Here, we report a new strategy to enhance homologous recombination in Arabidopsis. In Escherichia coli and Saccharomyces cerevisiae, hotspots that enhance homologous recombination nearby have been identified in regions close to sites associated with the blocking of DNA replication forks or with intensive transcriptional activity. In yeast, a recombination hotspot (HOT1) was found in a region spanning two non-transcribed spacers (NTS) between ribosomal RNA genes (rDNA), which contains both a replication fork barrier ( RFB) and the promoter for transcription of the 35S rRNA gene. Since rDNA has a common structure among eukaryotes, we analyzed the effect of the endogenous NTS on homologous mitotic recombination in a higher plant. We constructed transgenic lines of Arabidopsis containing this NTS and a recombination substrate, in which two 3'- and 5'-deleted uidA (beta-glucuronidase) genes with partially overlapping sequences are separated by a Hyg(r) gene. Reconstitution of functional uidA genes by homologous recombination was monitored by histochemical GUS staining. We found that recombination occurred more frequently in all organs tested in F (Fork block) lines transgenic for the NTS than in C (Control) lines without the NTS. The average number of GUS+ spots on leaves in F lines was more than nine-fold higher than in C lines. Furthermore, by genomic Southern analysis, post-recombinational molecules were detected in a transgenic line, F43, which had an extremely high number of GUS+ blue spots. These results strongly suggest that NTS-dependent enhancement of homologous recombination may be a common feature of higher plants as well as yeast.
authors.affiliation: Department of Molecular Biomechanics, The Graduate University for Advanced Studies, and National Institute for Basic Biology, 38 Nishigonaka, Myodaiji-cho, Okazaki 444-8585, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Urawa
authors.forename: M
authors.initials: M
authors.lastname: Hidaka
authors.forename: S
authors.initials: S
authors.lastname: Ishiguro
authors.forename: K
authors.initials: K
authors.lastname: Okada
authors.forename: T
authors.initials: T
authors.lastname: Horiuchi
mesh_terms: D017360:Arabidopsis / Q000235:genetics*; D018744:DNA, Plant / Q000235:genetics*; D021903:DNA, Ribosomal Spacer / Q000235:genetics*; D017930:Genes, Reporter; D008938:Mitosis / Q000235:genetics; D016254:Mutagenesis, Insertional; D018515:Plant Leaves / Q000235:genetics; D018517:Plant Roots / Q000235:genetics; D030821:Plants, Genetically Modified; D011995:Recombination, Genetic
chemical_list: D018744:DNA, Plant; D021903:DNA, Ribosomal Spacer