Interactions of the COP9 signalosome with the E3 ubiquitin ligase SCF^TIR1 in mediating auxin response

The COP9 signalosome is an evolutionary conserved multiprotein complex of unknown function that acts as a negative regulator of photomorphogenic seedling development in Arabidopsis. Here, we show that plants with reduced COP9 signalosome levels had decreased auxin response similar to loss-offunction mutants of the E3 ubiquitin ligase SCF^TIR1. Furthermore, we found that the COP9 signalosome and SCF^TIR1 interacted in vivo and that the COP9 signalosome was required for efficient degradation of PSIAA6, a candidate substrate of SCF^TIR1. Thus, the COP9 signalosome may play an important role in mediating E3 ubiquitin ligase-mediated responses.