Far-red light inhibits germination through DELLA-dependent stimulation of ABA synthesis and ABI3 activity.
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.
Piskurewicz
Urszula
U
Département de Biologie Végétale, Université de Genève, Genève 4, Switzerland.
Turecková
Veronika
V
Lacombe
Eric
E
Lopez-Molina
Luis
L
D000040:Abscisic Acid / Q000096:biosynthesis*; D017360:Arabidopsis / Q000528:radiation effects*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D051792:Basic Helix-Loop-Helix Proteins / Q000378:metabolism; D005786:Gene Expression Regulation; D018525:Germination / Q000528:radiation effects*; D008027:Light; D012097:Repressor Proteins / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism
D000040:Abscisic Acid; D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; C091601:ABI3 protein, Arabidopsis; C109555:GAI protein, Arabidopsis; C508468:RGA protein, Arabidopsis; C450823:RGL2 protein, Arabidopsis; C508068:At2g20180 protein, Arabidopsis