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DEVELOPMENT AND HORMONE ACTION

Abscisic Acid and Stress Signals Induce Viviparous1 Expression in Seed and Vegetative Tissues of Maize^1,[OA]

Department of Genetics, Development and Cell Biology, Iowa State University, Ames, Iowa 50011 (X.C., N.D., P.W.B.); Department of Plant Sciences, University of Oxford, Oxford OX1 3RB, United Kingdom (L.M.C., J.F.G.-M.); Biogemma, 63 170 Aubire, France (C.B.-P., B.K., P.P.); and Department of Horticultural Sciences, University of Florida, Gainesville, Florida 32611 (D.R.M.)

Viviparous1 (Vp1) encodes a B3 domain-containing transcription factor that is a key regulator of seed maturation in maize (Zea mays). However, the mechanisms of Vp1 regulation are not well understood. To examine physiological factors that may regulate Vp1 expression, transcript levels were monitored in maturing embryos placed in culture under different conditions. Expression of Vp1 decreased after culture in hormone-free medium, but was induced by salinity or osmotic stress. Application of exogenous abscisic acid (ABA) also induced transcript levels within 1 h in a dose-dependent manner. The Vp1 promoter fused to -glucuronidase or green fluorescent protein reproduced the endogenous Vp1 expression patterns in transgenic maize plants and also revealed previously unknown expression domains of Vp1. The Vp1 promoter is active in the embryo and aleurone cells of developing seeds and, upon drought stress, was also found in phloem cells of vegetative tissues, including cobs, leaves, and stems. Sequence analysis of the Vp1 promoter identified a potential ABA-responsive complex, consisting of an ACGT-containing ABA response element (ABRE) and a coupling element 1-like motif. Electrophoretic mobility shift assay confirmed that the ABRE and putative coupling element 1 components specifically bound proteins in embryo nuclear protein extracts. Treatment of embryos in hormone-free Murashige and Skoog medium blocked the ABRE-protein interaction, whereas exogenous ABA or mannitol treatment restored this interaction. Our data support a model for a VP1-dependent positive feedback mechanism regulating Vp1 expression during seed maturation.

² These authors contributed equally to the paper.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Philip W. Becraft (becraft{at}iastate.edu).

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www.plantphysiol.org/cgi/doi/10.1104/pp.106.091454

^* Corresponding author; e-mail becraft{at}iastate.edu; fax 515–294–6755.

Received October 18, 2006; accepted December 19, 2006; published January 5, 2007.

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