Abstract
Many aspects of plant biology depend on the ubiquitin proteasome system for degradation of regulatory proteins. Ubiquitin E3 ligases confer substrate specificity in this pathway, and SCF-type ligases comprise a major class of E3s. SCF ligases have four subunits: SKP1, CUL1, RBX1, and an F-box protein for substrate recognition. The Aux/IAAs are a well-characterized family of SCF substrates in plants. Here, we report characterization of a mutant isolated from a genetic screen in
Arabidopsis thaliana
designed to identify plants defective in degradation of an Aux/IAA fusion protein, Aux/IAA1-luciferase (IAA1-LUC). This mutant exhibited fourfold slower IAA1-LUC degradation compared with the progenitor line, and seedlings displayed altered auxin responses. Experiments identified the mutant as an allele of
CUL1
, named
cul1-7
. The
cul1-7
mutation affects the C terminus of the protein, results in reduced cul1-7 levels, and interferes with RBX1 interaction.
cul1-7
seedlings are defective in degradation of an endogenous SCF substrate, Repressor of
ga1-3
(RGA), and have altered responses to gibberellins.
cul1-7
seedlings exhibit slower degradation of the light-labile red/far-red photoreceptor phytochrome A and are photomorphogenic in the dark. This mutation represents the first reported allele of
CUL1
to directly affect subunit interactions at the CUL1 C terminus.