title: Evidence for karyoplasmic homeostasis during endoreduplication and a ploidy-dependent increase in gene transcription during tomato fruit growth.
abstract: Endopolyploidy is a widespread process that corresponds to the amplification of the genome in the absence of mitosis. In tomato, very high ploidy levels (up to 256C) are reached during fruit development, concomitant with very large cell sizes. Using cellular approaches (fluorescence and electron microscopy) we provide a structural analysis of endoreduplicated nuclei at the level of chromatin and nucleolar organisation, nuclear shape and relationship with other cellular organelles such as mitochondria. We demonstrate that endopolyploidy in pericarp leads to the formation of polytene chromosomes and markedly affects nuclear structure. Nuclei manifest a complex shape, with numerous deep grooves that are filled with mitochondria, affording a fairly constant ratio between nuclear surface and nuclear volume. We provide the first direct evidence that endopolyploidy plays a role in increased transcription of rRNA and mRNA on a per-nucleus basis. Overall, our results provide quantitative evidence in favour of the karyoplasmic theory and show that endoreduplication is associated with complex cellular organisation during tomato fruit development.
authors.affiliation: University of Bordeaux, UMR1332 Biologie du Fruit et Pathologie, BP 81, F-33140 Villenave d'Ornon,  France.
authors.forename: Matthieu
authors.initials: M
authors.lastname: Bourdon
authors.forename: Julien
authors.initials: J
authors.lastname: Pirrello
authors.forename: Catherine
authors.initials: C
authors.lastname: Cheniclet
authors.forename: Olivier
authors.initials: O
authors.lastname: Coriton
authors.forename: Mickaël
authors.initials: M
authors.lastname: Bourge
authors.forename: Spencer
authors.initials: S
authors.lastname: Brown
authors.forename: Adeline
authors.initials: A
authors.lastname: Moïse
authors.forename: Martine
authors.initials: M
authors.lastname: Peypelut
authors.forename: Valérie
authors.initials: V
authors.lastname: Rouyère
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Renaudin
authors.forename: Christian
authors.initials: C
authors.lastname: Chevalier
authors.forename: Nathalie
authors.initials: N
authors.lastname: Frangne
mesh_terms: D002467:Cell Nucleus / Q000235:genetics / Q000648:ultrastructure*; D048429:Cell Size; D002843:Chromatin / Q000648:ultrastructure; D062951:Endoreduplication; D005638:Fruit / Q000254:growth & development; D005784:Gene Amplification; D006706:Homeostasis; D017404:In Situ Hybridization, Fluorescence; D018551:Solanum lycopersicum / Q000235:genetics* / Q000254:growth & development* / Q000648:ultrastructure; D046529:Microscopy, Electron, Transmission; D008928:Mitochondria / Q000648:ultrastructure; D008938:Mitosis; D009697:Nucleolus Organizer Region / Q000648:ultrastructure; D011123:Polyploidy; D059007:Polytene Chromosomes / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D012335:RNA, Ribosomal / Q000096:biosynthesis; D014158:Transcription, Genetic; D015533:Transcriptional Activation
chemical_list: D002843:Chromatin; D012333:RNA, Messenger; D012335:RNA, Ribosomal