Abstract
F-Box (FBX) proteins are encoded by a multigene family present in major lineages of eukaryotes. A number of FBX proteins are shown to be subunits of SCF complex, a type of E3 ligases composed of SKP1, CULLIN, FBX and RBX1 proteins. The Arabidopsis SKP-LIKE (ASK) proteins are also members of a family and some of them interact with FBX proteins directly. To clarify how FBX and ASK proteins combine, we carried out a large-scale interaction analysis between FBX and ASK proteins using yeast two-hybrid assay (Y2H) in Arabidopsis thaliana. FBX proteins randomly chosen from those proteins that interacted with more than one ASK protein were further analyzed for their subcellular localization and in vivo interaction with ASK proteins. Furthermore, the expression profiles of FBX and ASK genes were compared. This work reveals that FBX proteins had a preference for interacting with ASK proteins depending on the domains they contain such as the FBX-associated (FBA) domain, the Kelch domain and leucine rich repeat (LRR). In addition, it was found that a single FBX protein could form multiple SCF complexes by interacting with several ASK proteins in many cases. Furthermore, it was suggested that the variation of SCF complexes were especially abundant in tissues related to male gametophyte and seed development. More than half of the FBX proteins studied did not interact with any of the ASK proteins, implying the necessity for certain regulations for their interaction in vivo and/or distinct roles from subunits of the SCF complex.
Highlights
Protein regulation is known to be an important system to allow adaptation to various abiotic and biotic stresses such as heat, drought and pathogens as well as for carrying out normal functions for survival
Specificity against FBX proteins was observed in Arabidopsis SKP-LIKE (ASK) proteins; eight ASK proteins (1–4 and 11–14) interacted with more than 40 FBX proteins, while other ones interacted with far fewer (Figure 1A)
This implies that other regions within ASK proteins may be responsible for the specificity against FBX proteins
Summary
Protein regulation is known to be an important system to allow adaptation to various abiotic and biotic stresses such as heat, drought and pathogens as well as for carrying out normal functions for survival. Ubiquitin (Ub)-mediated regulation is one of the key mechanisms for degradation and protein signaling in eukaryotes. Various proteins are regulated by the Ubmediated system in response to different environmental stresses and developmental signals such as the cell cycle and flowering [1,2,3,4,5,6]. Of the several types of E3 ligases, the SCF complex, composed of CULLIN, SKP1, RBX1 and FBX proteins, is the most variable. Numerous FBX genes have been identified in plants such as Arabidopsis (897 genes), rice (971 genes) and popular (425 genes) [10], because functional diversity within a gene family is thought to develop a prompt response to environmental changes in addition to the various signals involved in plant development [11,12]
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