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Publication Abstract from PubMed

Brassinosteroids (BRs) are vital plant steroid hormones sensed at the cell surface by a membrane signaling complex comprising the receptor kinase BRI1 and a SERK-family co-receptor kinase. Activation of this complex lead to dissociation of the inhibitor protein BKI1 from the receptor and to differential phosphorylation of BZR1/BES1 transcription factors by the glycogen synthase kinase 3 protein BIN2. Many phosphoproteins of the BR signaling pathway, including BRI1, SERKs, BKI1 and BZR1/BES1 can associate with 14-3-3 proteins. In this study, we use quantitative ligand binding assays to define the minimal 14-3-3 binding sites in the N-terminal lobe of the BRI1 kinase domain, in BKI1, and in BZR1 from Arabidopsis thaliana. All three motifs require to be phosphorylated to specifically bind 14-3-3s with mid- to low micromolar affinity. BR signaling components display minimal isoform preference within the 14-3-3 non-epsilon subgroup. 14-3-3lambda and 14-3-3omega isoform complex crystal structures reveal that BKI1 and BZR1 bind as canonical type II 14-3-3 linear motifs. Disruption of key amino acids in the phosphopeptide binding site through mutation impairs the interaction of 14-3-3lambda with all three linear motifs. Notably, quadruple loss-of-function mutants from the non-epsilon group exhibit gain-of-function brassinosteroid signaling phenotypes, suggesting a role for 14-3-3 proteins as overall negative regulators of the BR pathway. Collectively, our work provides further mechanistic and genetic evidence for the regulatory role of 14-3-3 proteins at various stages of the brassinosteroid signaling cascade.

Mechanistic insights into the function of 14-3-3 proteins as negative regulators of brassinosteroid signaling in Arabidopsis.,Obergfell E, Hohmann U, Moretti A, Chen H, Hothorn M Plant Cell Physiol. 2024 May 23:pcae056. doi: 10.1093/pcp/pcae056. PMID:38783418^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.