Interactions Between Two WD40 Repeat‐like Proteins and the NIGT1.1 Transcriptional Repressor in Arabidopsis Stress Gene Regulation

Gene regulation often depends upon WD40 repeat (WDR) proteins to serve as scaffolds in multi‐protein regulatory complexes. For example, WDR proteins can mediate dimerization of DNA‐binding transcription factors or they can assist in recruiting additional proteins, such as chromatin‐modifying enzymes, required for regulation of gene expression. We have identified two WD40 repeat‐like proteins in Arabidopsis that are highly conserved in plants, which we have named FBS INTERACTING PROTEINs (FBIPs) for their interaction with stress‐associated E3 ligase SCFFBS. Yeast two‐hybrid (Y2H) assays show that FBIP proteins also interact with NIGT1.1, a GARP‐type transcriptional repressor that regulates nitrate and phosphate starvation signaling and responses in plants. We further assessed the FBIP‐NIGT1.1 interaction with bimolecular fluorescence complementation (BiFC) experiments and found that partnering between these proteins occurs in the nucleus. Our current work investigates whether FBIP proteins interact with other GARP‐type repressors, for example the other three members of the NIGT1 family, which could suggest a broader role for FBIP proteins in gene regulation. Collectively, these interactions between SCFFBS, FBIP, and NIGT1 proteins delineate a previously unrecognized SCF‐connected transcription regulation module that works in the context of phosphate and nitrate starvation, and possibly other environmental stresses.