Isolation and characterization of cul1-7, a recessive allele of CULLIN1 that disrupts SCF function at the C terminus of CUL1 in Arabidopsis thaliana

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 ligascs 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 thauana designed to identify plants defective in degradation of an Aux/IAA fusion protein, Aux/IAA1-luciferase (IAA1-LUG). 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 cull-7 mutation affects the C terminus of the protein, results in reduced c.ull-7 levels, and interferes with RBX1 interaction, cull-7 seedlings are defective in degradation of an endogenous SCF substrate. Repressor of gal-3 (RGA), and have altered responses to gibberellins. cull-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. Copyright © 2009 by the Genetics Society of America.