title: Combined fluorescent and electron microscopic imaging unveils the specific properties of two classes of meiotic crossovers.
abstract: Crossovers (COs) shuffle genetic information and allow balanced segregation of homologous chromosomes during the first division of meiosis. In several organisms, mutants demonstrate that two molecularly distinct pathways produce COs. One pathway produces class I COs that exhibit interference (lowered probability of nearby COs), and the other pathway produces class II COs with little or no interference. However, the relative contributions, genomic distributions, and interactions of these two pathways are essentially unknown in nonmutant organisms because marker segregation only indicates that a CO has occurred, not its class type. Here, we combine the efficiency of light microscopy for revealing cellular functions using fluorescent probes with the high resolution of electron microscopy to localize and characterize COs in the same sample of meiotic pachytene chromosomes from wild-type tomato. To our knowledge, for the first time, every CO along each chromosome can be identified by class to unveil specific characteristics of each pathway. We find that class I and II COs have different recombination profiles along chromosomes. In particular, class II COs, which represent about 18% of all COs, exhibit no interference and are disproportionately represented in pericentric heterochromatin, a feature potentially exploitable in plant breeding. Finally, our results demonstrate that the two pathways are not independent because there is interference between class I and II COs.
authors.affiliation: Department of Biology, Colorado State University, Fort Collins, CO 80523-1878; and lorinda.anderson@colostate.edu.
authors.forename: Lorinda K
authors.initials: LK
authors.lastname: Anderson
authors.affiliation: Department of Biology, Colorado State University, Fort Collins, CO 80523-1878; and.
authors.forename: Leslie D
authors.initials: LD
authors.lastname: Lohmiller
authors.affiliation: Department of Biology, Colorado State University, Fort Collins, CO 80523-1878; and.
authors.forename: Xiaomin
authors.initials: X
authors.lastname: Tang
authors.affiliation: Department of Biology, Colorado State University, Fort Collins, CO 80523-1878; and.
authors.forename: D Boyd
authors.initials: DB
authors.lastname: Hammond
authors.affiliation: Department of Biology, Colorado State University, Fort Collins, CO 80523-1878; and.
authors.forename: Lauren
authors.initials: L
authors.lastname: Javernick
authors.affiliation: Department of Biology, Colorado State University, Fort Collins, CO 80523-1878; and.
authors.forename: Lindsay
authors.initials: L
authors.lastname: Shearer
authors.affiliation: INRA, UMR 0320/UMR 8120 Génétique Végétale, F-91190 Gif-sur-Yvette, France.
authors.forename: Sayantani
authors.initials: S
authors.lastname: Basu-Roy
authors.affiliation: INRA, UMR 0320/UMR 8120 Génétique Végétale, F-91190 Gif-sur-Yvette, France.
authors.forename: Olivier C
authors.initials: OC
authors.lastname: Martin
authors.affiliation: INRA, UMR 0320/UMR 8120 Génétique Végétale, F-91190 Gif-sur-Yvette, France.
authors.forename: Matthieu
authors.initials: M
authors.lastname: Falque
mesh_terms: D032461:Chromosomes, Plant / Q000235:genetics; D003434:Crossing Over, Genetic; D021621:Imaging, Three-Dimensional; D018551:Solanum lycopersicum / Q000166:cytology* / Q000235:genetics* / Q000648:ultrastructure; D008540:Meiosis / Q000235:genetics*; D049469:Meiotic Prophase I; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D010940:Plant Proteins / Q000378:metabolism; D013573:Synaptonemal Complex
chemical_list: D010940:Plant Proteins
keywords: MLH1; MUS81; genetic interference; recombination nodule; synaptonemal complex