The Arabidopsis
SLY1
(
SLEEPY1
) gene positively regulates gibberellin (GA) signaling. Positional cloning of
SLY1
revealed
that it encodes a putative F-box protein. This result suggests that SLY1 is the F-box subunit of an SCF E3 ubiquitin ligase
that regulates GA responses. The DELLA domain protein RGA (repressor of
ga1-3
) is a repressor of GA response that appears
to undergo GA-stimulated protein degradation. RGA is a potential substrate of SLY1, because
sly1
mutations cause a
significant increase in RGA protein accumulation even after GA treatment. This result suggests SCF
SLY1
-targeted degradation
of RGA through the 26S proteasome pathway. Further support for this model is provided by the observation that an
rga
null allele partially suppresses the
sly1-10
mutant phenotype. The predicted SLY1 amino acid sequence is highly conserved
among plants, indicating a key role in GA response.