Article
- The EMBO Journal (2009) 28, 2259 - 2271
- doi:10.1038/emboj.2009.170
Published online: 25 June 2009
Subject Categories:
Far-red light inhibits germination through DELLA-dependent stimulation of ABA synthesis and ABI3 activity
Urszula Piskurewicz1,
Veronika Ture
ková2,
Eric Lacombe3 and Luis Lopez-Molina1
- Département de Biologie Végétale, Université de Genève, Genève 4, Switzerland
- Laboratory of Growth Regulators, Palacky University and Institute of Experimental Botany ASCR, Olomouc, Czech Republic
- Biochimie & Physiologie Moléculaire des Plantes, Unité Mixte de Recherche CNRS/INRA, Université Montpellier II, SupAgro, Montpellier Cedex 1, France
Correspondence to:
Luis Lopez-Molina, Département de Biologie Végétale, Université de Genève, 30, quai Ernest-Ansermet—Sciences III, 1211 Genève 4, Switzerland. Tel.: +41 22 379 3206; Fax: +41 22 379 3205; E-mail: luis.lopezmolina@unige.ch
Received 19 March 2009; Accepted 27 May 2009
Abstract
Under the canopy, far-red (FR) light represses seed germination by inactivating phytochrome photoreceptors. This elicits a decrease in gibberellins (GA) levels and an increase in abscisic acid (ABA) levels. GA promotes germination by enhancing the proteasome-mediated destruction of DELLA repressors. ABA prevents germination by stimulating the expression of ABI repressors. How phytochromes elicit changes in hormone levels or how GA- and ABA-dependent signals are coordinated to repress germination remains poorly understood. We show that repression of germination by FR light involves stabilized DELLA factors GAI, RGA and RGL2 that stimulate endogenous ABA synthesis. In turn, ABA blocks germination through the transcription factor ABI3. The role of PIL5, a basic helix-loop-helix transcription factor stimulating GAI and RGA expression, is significant, provided GA synthesis is high enough; otherwise, high GAI and RGA protein levels persist to block germination. Under white light, GAI and RGA driven by the RGL2 promoter can substitute for RGL2 to promote ABA synthesis and repress germination, consistent with the recent findings with RGL2. The three DELLA factors inhibit testa rupture whereas ABI3 blocks endosperm rupture.
Keywords:
- abscisic acid,
- DELLA,
- gibberellins,
- phytochrome,
- seed germination
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