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UFO in the Arabidopsis inflorescence apex is required for floral-meristem identity and bract suppression

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Abstract

The UNUSUAL FLORAL ORGANS (UFO) gene of Arabidopsis encodes an F-box protein required for the determination of floral-organ and floral-meristem identity. Mutation of UFO leads to dramatic changes in floral-organ type which are well-characterized whereas inflorescence defects are more subtle and less understood. These defects include an increase in the number of secondary inflorescences, nodes that alternate between forming flowers and secondary inflorescences, and nodes in which a single flower is subtended by a bract. Here, we show how inflorescence defects correlate with the abnormal development of floral primordia and establish a temporal requirement for UFO in this process. At the inflorescence apex of ufo mutants, newly formed primordia are initially bract-like. Expression of the floral-meristem identity genes LFY and AP1 are confined to a relatively small adaxial region of these primordia with expression of the bract-identity marker FIL observed in cells that comprise the balance of the primordia. Proliferation of cells in the adaxial region of these early primordia is delayed by several nodes such that primordia appear “chimeric” at several nodes, having visible floral and bract components. However, by late stage 2 of floral development, growth of the bract generally ceases and is overtaken by development of the floral primordium. This abnormal pattern of floral meristem development is not rescued by expression of UFO from the AP1 promoter, indicating that UFO is required prior to AP1 activation for normal development of floral primordia. We propose that UFO and LFY are jointly required in the inflorescence meristem to both promote floral meristem development and inhibit, in a non-cell autonomous manner, growth of the bract.

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Abbreviations

Col:

Columbia

IM:

Inflorescence meristem

Ler :

Landsberg erecta

SCF:

Skp1-Cullin-F-box

SEM:

Scanning electron microscopy

SAM:

Shoot apical meristem

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Acknowledgements

We are grateful to Ilha Lee, Takuji Wade, and Detlef Weigel for their gift of AP1::UFO, and AP1::UFO ufo-2 transgenic plants. We also thank Detlef Weigel for providing 35S::UFO transgenic plants and thank Kiyotaka Okada for providing the fil-1 mutant. We thank members of the laboratory for helpful discussions during the course of this work. George Haughn was supported by both Strategic and Discovery grants from the Natural Sciences and Engineering Research Council of Canada.

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  1. Department of Botany, University of British Columbia, Vancouver, British Columbia, V6T 1Z4, Canada

    Shelley R. Hepworth, Jennifer E. Klenz & George W. Haughn

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  1. Shelley R. Hepworth
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  2. Jennifer E. Klenz
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  3. George W. Haughn
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Correspondence to George W. Haughn.

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Shelley R. Hepworth and Jennifer E. Klenz contributed equally to this work.

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Hepworth, S.R., Klenz, J.E. & Haughn, G.W. UFO in the Arabidopsis inflorescence apex is required for floral-meristem identity and bract suppression. Planta 223, 769–778 (2006). https://doi.org/10.1007/s00425-005-0138-3

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