Plant F-box Proteins – Judges between Life and Death

Selective protein degradation through the ubiquitin–26S proteasome system is a key mechanism for post-translational control of regulatory proteins in all eukaryotes. The pivotal components in this system are the multi-subunit E3 Ub-ligase enzymes responsible for specific recognition and ubiquitination of degradation targets. In this review, we focus on plant F-box proteins which confer specificity to the SCF-type E3 enzyme complexes. F-box proteins represent one of the largest and most heterogeneous superfamilies in plants, with hundreds of different representatives exposing an extensive variability of C-terminal target-binding domains, and as such, modulating almost every aspect of plant growth and development. Since the first reports on plant F-box proteins over a decade ago, a lot of progress has been made in our understanding of their relevance for plant physiology. In this review, we combine well-established knowledge with the most recent advances related to plant F-box proteins and their role in plant development, hormone signaling and defense pathways. We also elaborate on the yet poorly described carbohydrate-binding plant F-box proteins presumably targeting glycoproteins for proteasomal degradation.