title: Meiotic Crossing Over in Maize Knob Heterochromatin.
abstract: There is ample evidence that crossing over is suppressed in heterochromatin associated with centromeres and nucleolus organizers (NORs). This characteristic has been attributed to all heterochromatin, but the generalization may not be justified. To investigate the relationship of crossing over to heterochromatin that is not associated with centromeres or NORs, we used a combination of fluorescencein situhybridization of the maize 180-bp knob repeat to show the locations of knob heterochromatin and fluorescent immunolocalization of MLH1 protein and AFD1 protein to show the locations of MLH1 foci on maize synaptonemal complexes (SCs, pachytene chromosomes). MLH1 foci correspond to the location of recombination nodules (RNs) that mark sites of crossing over. We found that MLH1 foci occur at similar frequencies per unit length of SC in interstitial knobs and in the 1 µm segments of SC in euchromatin immediately to either side of interstitial knobs. These results indicate not only that crossing over occurs within knob heterochromatin, but also that crossing over is not suppressed in the context of SC length in maize knobs. However, because there is more DNA per unit length of SC in knobs compared to euchromatin, crossing over is suppressed (but not eliminated) in knobs in the context of DNA length compared to adjacent euchromatin.
authors.affiliation: Department of Biology, Colorado State University, Fort Collins, Colorado 80523 stephen.stack@colostate.edu.
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Stack
authors.affiliation: Department of Biology, Colorado State University, Fort Collins, Colorado 80523.
authors.forename: Lindsay A
authors.initials: LA
authors.lastname: Shearer
authors.affiliation: Department of Biology, Colorado State University, Fort Collins, Colorado 80523.
authors.forename: Leslie
authors.initials: L
authors.lastname: Lohmiller
authors.affiliation: Department of Biology, Colorado State University, Fort Collins, Colorado 80523.
authors.forename: Lorinda K
authors.initials: LK
authors.lastname: Anderson
mesh_terms: D032461:Chromosomes, Plant / Q000235:genetics; D003434:Crossing Over, Genetic; D006570:Heterochromatin / Q000235:genetics*; D008540:Meiosis / Q000235:genetics*; D000070957:MutL Protein Homolog 1 / Q000235:genetics; D013573:Synaptonemal Complex / Q000235:genetics; D003313:Zea mays / Q000235:genetics*
chemical_list: D006570:Heterochromatin; D000070957:MutL Protein Homolog 1
keywords: crossing over; heterochromatin; knobs; maize; synaptonemal complex