title: Defining multiple, distinct, and shared spatiotemporal patterns of DNA replication and endoreduplication from 3D image analysis of developing maize (Zea mays L.) root tip nuclei.
abstract: Spatiotemporal patterns of DNA replication have been described for yeast and many types of cultured animal cells, frequently after cell cycle arrest to aid in synchronization. However, patterns of DNA replication in nuclei from plants or naturally developing organs remain largely uncharacterized. Here we report findings from 3D quantitative analysis of DNA replication and endoreduplication in nuclei from pulse-labeled developing maize root tips. In both early and middle S phase nuclei, flow-sorted on the basis of DNA content, replicative labeling was widely distributed across euchromatic regions of the nucleoplasm. We did not observe the perinuclear or perinucleolar replicative labeling patterns characteristic of middle S phase in mammals. Instead, the early versus middle S phase patterns in maize could be distinguished cytologically by correlating two quantitative, continuous variables, replicative labeling and DAPI staining. Early S nuclei exhibited widely distributed euchromatic labeling preferentially localized to regions with weak DAPI signals. Middle S nuclei also exhibited widely distributed euchromatic labeling, but the label was preferentially localized to regions with strong DAPI signals. Highly condensed heterochromatin, including knobs, replicated during late S phase as previously reported. Similar spatiotemporal replication patterns were observed for both mitotic and endocycling maize nuclei. These results revealed that maize euchromatin exists as an intermingled mixture of two components distinguished by their condensation state and replication timing. These different patterns might reflect a previously described genome organization pattern, with "gene islands" mostly replicating during early S phase followed by most of the intergenic repetitive regions replicating during middle S phase.
authors.affiliation: Department of Biological Science, Florida State University, 319 Stadium Drive, King Life Sciences Building, Tallahassee, FL, 32306-4295, USA. bass@bio.fsu.edu.
authors.forename: Hank W
authors.identifier: http://orcid.org/0000-0003-0522-0881
authors.initials: HW
authors.lastname: Bass
authors.affiliation: Department of Biological Science, Florida State University, 319 Stadium Drive, King Life Sciences Building, Tallahassee, FL, 32306-4295, USA.
authors.forename: Gregg G
authors.initials: GG
authors.lastname: Hoffman
authors.affiliation: Department of Plant and Microbial Biology, North Carolina State University, Raleigh, NC, 27695-7612, USA.
authors.forename: Tae-Jin
authors.initials: TJ
authors.lastname: Lee
authors.affiliation: Department of Plant and Microbial Biology, North Carolina State University, Raleigh, NC, 27695-7612, USA.
authors.forename: Emily E
authors.initials: EE
authors.lastname: Wear
authors.affiliation: Department of Biological Science, Florida State University, 319 Stadium Drive, King Life Sciences Building, Tallahassee, FL, 32306-4295, USA.
authors.forename: Stacey R
authors.initials: SR
authors.lastname: Joseph
authors.affiliation: Department of Horticultural Science, North Carolina State University, Raleigh, NC, 27695-7609, USA.
authors.forename: George C
authors.initials: GC
authors.lastname: Allen
authors.affiliation: Department of Plant and Microbial Biology, North Carolina State University, Raleigh, NC, 27695-7612, USA.
authors.forename: Linda
authors.initials: L
authors.lastname: Hanley-Bowdoin
authors.affiliation: Department of Plant and Microbial Biology, North Carolina State University, Raleigh, NC, 27695-7612, USA.
authors.forename: William F
authors.initials: WF
authors.lastname: Thompson
mesh_terms: D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism; D004261:DNA Replication / Q000235:genetics*; D042522:DNA Replication Timing / Q000235:genetics; D018744:DNA, Plant / Q000096:biosynthesis / Q000235:genetics; D062951:Endoreduplication / Q000235:genetics*; D017343:Genes, Plant; D021621:Imaging, Three-Dimensional; D018519:Meristem / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D008954:Models, Biological; D016196:S Phase / Q000235:genetics; D003313:Zea mays / Q000235:genetics* / Q000254:growth & development* / Q000378:metabolism
chemical_list: D018744:DNA, Plant
keywords: Cell cycle; DNA synthesis; Grass