Immunophilin-like FKBP42/TWISTED DWARF1 Interacts with the Receptor Kinase BRI1 to Regulate Brassinosteroid Signaling in Arabidopsis

Abstract

Mutation of the immunophilin-like FK506-binding protein TWISTED DWARF1 (FKBP42/TWD1) causes dwarf and twisted-organ phenotypes in Arabidopsis. However, the function of FKBP42 is not fully understood at the molecular level. Using genetic, physiological and immunological experiments, we show here that FKBP42 is necessary for brassinosteroid (BR) signal transduction. The twd1 mutant showed reduced BR sensitivity in growth responses and activation of the BZR1 transcription factor. However, twd1 showed normal responses to an inhibitor of BIN2/GSK3, suggesting that twd1 has defect upstream of BIN2 in the BR signaling pathway. In vitro and in vivo assays showed that TWD1 interacts physically with the kinase domains of the BR receptor kinases BRI1 and BAK1. TWD1 is not required for normal localization of BRI1-GFP to the plasma membrane or for activation of the flagellin receptor kinase FLS2. Our results suggest that FKBP42/TWD1 plays a specific role in the activation of BRI1 receptor kinase.

HSP90 and co‐chaperones: a multitaskers’ view on plant hormone biology

“…Two independent studies reported that TWD1 interacts directly with the kinase domain of BRI1 and BAK1 in a BR-independent manner [108,109]. However, TWD1 appears not to regulate BR co-receptor maturation at the ER, as suggested by their unchanged PM localization and abundance in twd1 mutants [108,109]. Instead, TWD1 was found to be required for efficient auto-phosphorylation of both co-receptors upon BR perception and therefore their signal transduction activity [109] (Fig.…”

“…Interestingly, the twd1 mutant reacted to treatment with the minimal flagellin peptide epitope flg22 rather more strongly than wild type [108]. This may be in line with the known antagonism between BR and flg22 signaling or related to a negative role of TWD1 chaperone activity to regulate BAK1 availability for immune complex formation [103,108]. Interestingly, SGT1b was found to be dispensable for BR signaling and the interference with flg22 induced gene regulation, while auxin, gibberellic acid (GA), and jasmonate treatment blocked flg22 signaling in a SGT1bdependent manner [14].…”

“…Furthermore, it is important to note that the MAMP-signaling branch of BAK1 in conjunction with the bacterial flagellin receptor flagellin insensitive 2 (FLS2) is not dependent on TWD1 [108]. Interestingly, the twd1 mutant reacted to treatment with the minimal flagellin peptide epitope flg22 rather more strongly than wild type [108]. This may be in line with the known antagonism between BR and flg22 signaling or related to a negative role of TWD1 chaperone activity to regulate BAK1 availability for immune complex formation [103,108].…”

Q&A: what are brassinosteroids and how do they act in plants?

“…Fully addressing this question will require detailed elucidation of structure of the full-length complex. New components are being identified in brassinosteroid signalling and understanding of how they are integrated with other signalling pathways will be important to gain a comprehensive and systematic view of brassinosteroid functions in various plants [49, 50]. A full elucidation of brassinosteroid signalling events and their integration with other signalling pathways will enable brassinosteroid to be applied in agriculture.…”

Diverse roles of SERK family genes in plant growth, development and defense response

“…Recently two group reported that an immunophilin-like FK506-binding protein twisted dwarf1 (TWD1) physically interacts with BRI1 and BAK1 to modulate BR signal transduction (Chaiwanon et al, 2016;Zhao et al, 2016). The TWD1 loss-of-function mutants display reduced cell elongation, twisted organ and dark green leaf phenotype, which are similar to BR-signaling or biosynthesis mutants.…”