Current Understanding of the CRL1 Complex in Arabidopsis

Ubiquitination is a post-translational modification involved in diverse cellular processes in eukaryotes. Among three kinds of enzymes (E1, E2, and E3) involved in ubiquitination, the E3 ubiquitin ligase family possesses a large number of members (up to 1400) and serves as a major determinant for substrate specificity. As a type of E3 ligase, cullin-RING E3 ligase (CRL) forms multi-subunit complexes classified into three types, CRL1, CRL3, and CRL4, in Arabidopsis . Of E3 enzymes, the CRL1 complex, also known as the SCF complex, is the largest family and has been most fully characterized so far. Studies of the biological role of CRL1 have mainly concentrated on the functional elucidation of F-box proteins, serving as substrate receptors of CRL1. F-box proteins possess an N-terminal F-box motif consisting of 40–50 amino acids and a variable C-terminal substrate-interacting domain. An F-box domain and a substrate-interacting domain are responsible for the interaction of SKP1 as an adaptor of CRL1 and the target protein(s) to be ubiquitinated, respectively. There are many F-box proteins (e.g., ~ 690 members in Arabidopsis ), and CRL1 complexes generated from diverse F-box proteins are widely involved in most events occurring in plant cells. In this study, we review the current knowledge of and future prospects for CRL1 complexes with our main focus on F-box proteins, which function in developmental processes, hormone responses, and biotic/abiotic stress responses in Arabidopsis . Our review will enable a broadening of the understanding of the functional relationships between the CRL1-mediated ubiquitination process and Arabidopsis cellular responses.