Wheat F-box protein recruits proteins and regulates their abundance during wheat spike development

Abstract F-box proteins, components of the Skp1-Cullin1-F-box (SCF) protein E3 ubiquitin ligase complex, serve as the variable component responsible for substrate recognition and recruitment in SCF-mediated proteolysis. F-box proteins interact with Skp1 through the F-box motif and with ubiquitination substrates through C-terminal protein interaction domains. F-box proteins regulate plant development, various hormonal signal transduction processes, circadian rhythm, and cell cycle control. We isolated an F-box protein gene from wheat spikes at the onset of flowering. The Triticum aestivum cyclin F-box domain (TaCFBD) gene showed elevated expression levels during early inflorescence development and under cold stress treatment. TaCFBD green fluorescent protein signals were localized in the cytoplasm and plasma membrane. We used yeast two-hybrid screening to identify proteins that potentially interact with TaCFBD. Fructose bisphosphate aldolase, aspartic protease, VHS, glycine-rich RNA-binding protein, and the 26S proteasome non-ATPase regulatory subunit were positive candidate proteins. The bimolecular fluorescence complementation assay revealed the interaction of TaCFBD with partner proteins in the plasma membranes of tobacco cells. Our results suggest that the TaCFBD protein acts as an adaptor between target substrates and the SCF complex and provides substrate specificity to the SCF of ubiquitin ligase complexes.