The COP9 signalosome (CSN) is an evolutionarily conserved protein complex that resembles the lid subcomplex of proteasomes. Through its ability to regulate specific proteasome-mediated protein degradation events, CSN controls multiple aspects of development. Here we report subunit 4 of COP9 signalosome (CSN4) interacts with some subunits of SCF complex, affecting the deneddylation of CUL4 and CUL1,thus cause abnormal degradation of several downstream substrates in both light and auxin signaling pathway.This study advances our understanding of the molecular interactions between SCF and CSN complex in Arabidopsis.