Multiple phytochrome-interacting bHLH transcription factors repress premature seedling photomorphogenesis in darkness.
BACKGROUND
An important contributing factor to the success of terrestrial flowering plants in colonizing the land was the evolution of a developmental strategy, termed skotomorphogenesis, whereby postgerminative seedlings emerging from buried seed grow vigorously upward in the subterranean darkness toward the soil surface.


RESULTS
Here we provide genetic evidence that a central component of the mechanism underlying this strategy is the collective repression of premature photomorphogenic development in dark-grown seedlings by several members of the phytochrome (phy)-interacting factor (PIF) subfamily of bHLH transcription factors (PIF1, PIF3, PIF4, and PIF5). Conversely, evidence presented here and elsewhere collectively indicates that a significant component of the mechanism by which light initiates photomorphogenesis upon first exposure of dark-grown seedlings to irradiation involves reversal of this repression by rapid reduction in the abundance of these PIF proteins, through degradation induced by direct interaction of the photoactivated phy molecule with the transcription factors.


CONCLUSIONS
We conclude that bHLH transcription factors PIF1, PIF3, PIF4, and PIF5 act as constitutive repressors of photomorphogenesis in the dark, action that is rapidly abrogated upon light exposure by phy-induced proteolytic degradation of these PIFs, allowing the initiation of photomorphogenesis to occur.
Leivar
Pablo
P
Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720, USA.
Monte
Elena
E
Oka
Yoshito
Y
Liu
Tiffany
T
Carle
Christine
C
Castillon
Alicia
A
Huq
Enamul
E
Quail
Peter H
PH
D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism; D003624:Darkness; D018506:Gene Expression Regulation, Plant; D008027:Light; D009024:Morphogenesis / Q000528:radiation effects*; D010829:Physiological Phenomena; D010834:Phytochrome / Q000378:metabolism*; D036226:Seedlings / Q000235:genetics / Q000254:growth & development* / Q000502:physiology; D015398:Signal Transduction
D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D010834:Phytochrome; C508068:At2g20180 protein, Arabidopsis; C116162:PIF3 protein, Arabidopsis