title: Molecular basis for three-dimensional elaboration of the Aquilegia petal spur.
abstract: By enforcing specific pollinator interactions, Aquilegia petal nectar spurs maintain reproductive isolation between species. Spur development is the result of three-dimensional elaboration from a comparatively two-dimensional primordium. Initiated by localized, oriented cell divisions surrounding the incipient nectary, this process creates a pouch that is extended by anisotropic cell elongation. We hypothesized that the development of this evolutionary novelty could be promoted by non-mutually exclusive factors, including (i) prolonged, KNOX-dependent cell fate indeterminacy, (ii) localized organ sculpting and/or (iii) redeployment of hormone-signalling modules. Using cell division markers to guide transcriptome analysis of microdissected spur tissue, we present candidate mechanisms underlying spur outgrowth. We see dynamic expression of factors controlling cell proliferation and hormone signalling, but no evidence of contribution from indeterminacy factors. Transcriptome dynamics point to a novel recruitment event in which auxin-related factors that normally function at the organ margin were co-opted to this central structure. Functional perturbation of the transition between cell division and expansion reveals an unexpected asymmetric component of spur development. These findings indicate that the production of this three-dimensional form is an example of organ sculpting via localized cell division with novel contributions from hormone signalling, rather than a product of prolonged indeterminacy.
authors: Department of Organismic and Evolutionary Biology, Harvard University, 16 Divinity Ave., Cambridge, MA 02138, USA.
authors: Levi
authors: L
authors: Yant
authors: Department of Organismic and Evolutionary Biology, Harvard University, 16 Divinity Ave., Cambridge, MA 02138, USA.
authors: Silvio
authors: S
authors: Collani
authors: Department of Organismic and Evolutionary Biology, Harvard University, 16 Divinity Ave., Cambridge, MA 02138, USA.
authors: Joshua
authors: J
authors: Puzey
authors: Department of Organismic and Evolutionary Biology, Harvard University, 16 Divinity Ave., Cambridge, MA 02138, USA.
authors: Clara
authors: C
authors: Levy
authors: Department of Organismic and Evolutionary Biology, Harvard University, 16 Divinity Ave., Cambridge, MA 02138, USA ekramer@oeb.harvard.edu.
authors: Elena M
authors: EM
authors: Kramer
mesh_terms: D016880:Anisotropy; D031884:Aquilegia / Q000166:cytology / Q000235:genetics / Q000254:growth & development*; D049109:Cell Proliferation; D035264:Flowers / Q000166:cytology / Q000235:genetics / Q000254:growth & development*; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D020868:Gene Silencing; D007210:Indoleacetic Acids / Q000378:metabolism; D010937:Plant Growth Regulators / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D010942:Plant Viruses / Q000235:genetics; D054817:Pollination; D012333:RNA, Messenger / Q000378:metabolism; D059467:Transcriptome
chemical_list: D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; D010940:Plant Proteins; D012333:RNA, Messenger
keywords: Aquilegia; TCP4; gene expression; hormones; organ shape; virus-induced gene silencing