The ALF4 protein is a regulator of SCF E3 ligases

The cullin-RING E3 ligases (CRLs) regulate diverse cellular processes in all eukaryotes. CRL activity is controlled by several proteins or protein complexes, including NEDD8, CAND1, and the CSN Recently, a mammalian protein called Glomulin (GLMN) was shown to inhibit CRLs by binding to the RING BOX (RBX1) subunit and preventing binding to the ubiquitin-conjugating enzyme. Here, we show that ABERRANT LATERAL ROOT FORMATION4 (ALF4) is an ortholog of GLMN The mutant exhibits a phenotype that suggests defects in plant hormone response. We show that ALF4 binds to RBX1 and inhibits the activity of SCF, an E3 ligase responsible for degradation of the Aux/IAA transcriptional repressors. , the mutation destabilizes the CUL1 subunit of the SCF Reduced CUL1 levels are associated with increased levels of the Aux/IAA proteins as well as the DELLA repressors, substrate of SCF We propose that the phenotype is partly due to increased levels of the Aux/IAA and DELLA proteins.