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WIREs Dev Biol
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Auxin and cytokinin act during gynoecial patterning and the development of ovules from the meristematic medial domain

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The gynoecium is the female reproductive structure of flowering plants, and is the site of ovule and seed development. The gynoecium is critical for reproductive competence and for agricultural productivity in many crop plants. In this review we focus on molecular aspects of the development of the Arabidopsis thaliana gynoecium. We briefly introduce gynoecium structure and development and then focus on important research advances published within the last year. We highlight what has been learned recently with respect to: (1) the role of auxin in the differential development of the medial and lateral domains of the Arabidopsis gynoecium; (2) the interaction between cytokinin and auxin during gynoecial development; (3) the role of auxin in the termination of the floral meristem and in the transition of floral meristem to gynoecium; and (4) recent studies that suggest a degree of evolutionary conservation of auxin mechanisms during gynoecial development in other eudicots. WIREs Dev Biol 2015, 4:555–571. doi: 10.1002/wdev.193 This article is categorized under: Establishment of Spatial and Temporal Patterns > Regulation of Size, Proportion, and Timing Gene Expression and Transcriptional Hierarchies > Regulatory Mechanisms Plant Development > Inflorescence, Flower, and Fruit Development
Structural components along the apical/basal and medial/lateral axes of the Arabidopsis gynoecium. (a) A scanning electron microscopic image of a mature Arabidopsis gynoecium. The stigma (stg), style (sty), carpel valve (cv), abaxial replum (abr), gynophore (gn), ovary (ovy), and valve margin/dehiscence zone (dz) are indicated. (b,c) False‐colored confocal gynoecial cross sections. (b) A stage 11 cross section. A plane of symmetry (indicated with a dashed line) divides the gynoecium into two component carpels. Ovules (ov) and septum (s) are indicated. (c) A stage 8 cross section. Medial and lateral domains are indicated. The carpel margin meristem/medial ridge (mr) is false colored pink. (d) A scanning electron microscopic image of a developing gynoecium from a stage 7 flower. Dashed line indicates plane of symmetry that bisects the medial domain. (e,f) Stage 7 floral cross sections from in situ hybridization experiments. (e) CRC expression (brown product) is detected in the two lateral domains. (f) STM expression is detected in the medial domain. (Panels (a), (b), and (c) are reprinted with permission from Ref . Panel (d) is reprinted with permission from Ref )
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A model of ovule formation from the meristematic medial domain as proposed by Galbiati et al. See text for details. (Reprinted with permission from Ref )
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Diagrammatic representation of proposed patterns of auxin transport in the lateral and medial domains of a stage 7 gynoecium. (a) In the lateral domains auxin is transported predominantly via the PIN1 transporter and follows the ‘reverse fountain’ model. Auxin flow in the abaxial and adaxial epidermal cell layers is toward the apex. Green circles indicate the lateral domain DR5 response foci. (b) In the medial domain the flow of auxin in the abaxial epidermis is similarly toward the apex. However, in the adaxial epidermis and in subepidermal cells auxin transport is less polarized resulting in a less canalized (channeled) flow of auxin and in weaker and later‐forming DR5 foci (smaller green dots). Note: the confocal longitudinal gynoecium images in (a) and (b) are for diagrammatic purposes and are both images of an oblique lateral plane section. (c,d) A diagram of a cross‐sectional view of a stage 7 gynoecium. The dotted line in (a) and (b) indicates the plane of section for which auxin flows are represented in panels (a) and (b), respectively.
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Establishment of Spatial and Temporal Patterns > Regulation of Size, Proportion, and Timing
Gene Expression and Transcriptional Hierarchies > Regulatory Mechanisms
Plant Development > Inflorescence, Flower, and Fruit Development