Brassinosteroid nuclear signaling recruits HSP90 activity

Abstract

SummaryHeat shock protein 90 (HSP90) controls a number of developmental circuits, and serves a sophisticated and highly regulatory function in signaling pathways. Brassinosteroids (BRs) control many aspects of plant development.Genetic, physiological, cytological, gene expression, live cell imaging, and pharmacological approaches provide conclusive evidence for HSP90 involvement in Arabidopsis thaliana BR signaling.Nuclear-localized HSP90s translocate to cytoplasm when their activity is blocked by the HSP90 inhibitor geldanamycin (GDA). GDA treatment promoted the export of BIN2, a regulator of BR signaling, from the nucleus into the cytoplasm, indicating that active HSP90 is required to sustain BIN2 in the nucleus. HSP90 nuclear localization was inhibited by brassinolide (BL). HSP90s interact with BIN2 in the nucleus of untreated cells and in the cytoplasm of BL-treated cells, showing that the site-specific action of HSP90 on BIN2 is controlled by BRs. GDA and BL treatments change the expression of a common set of previously identified BRresponsive genes. This highlights the effect of active HSP90s on the regulation of BR-responsive genes. Our observations reveal that HSP90s have a central role in sustaining BIN2 nuclear function.We propose that BR signaling is mediated by HSP90 activity and via trafficking of BIN2-HSP90 complexes into the cytoplasm.

Heat shock protein 90 acts in brassinosteroid signaling through interaction with BES1/BZR1 transcription factor

“…protect BES1 against BIN2 kinase, recruiting PP2A to dephosphorylate it, or both. However, HSP90 is also necessary for nuclear retention and activity control of BIN2 kinase (Samakovli et al, 2014). Therefore, the role of HSP90 in controlling BES1 phosphorylation state might be more complicated we might assume.…”

“…They regulate BR responsive genes such as CPD and DWF4 (Samakovli et al, 2014;Shigeta et al, 2014). To date, it has remained indeterminate which portions of BES1 protein are responsible for the binding to HSP90.…”

“…Furthermore, HSP90.1 to HSP90.4 are highly conserved mutually with more than 85% amino acid sequence identity. Recently, Samakovli et al (2014) reported that HSP90 interacts with a BR signaling component, BIN2 kinase, to modulate its nuclear retention. Independently of their study, HSP90 was also found to bind to BES1 (Lachowiec et al, 2013;Shigeta et al, 2014).…”

Transcriptome analysis reveals the regulation of brassinosteroids on petal growth in Gerbera hybrida

“…In Arabidopsis , HSP90, as a molecular chaperone, contributes to BR-mediated gene expression through complex formation with two major TFs, BZR1 and BES1 (Samakovli et al, 2014; Shigeta et al, 2015). A recent study reported that HSP90 is pivotal in the transition from vegetative to reproductive phase in Arabidopsis and that depletion of HSP90 mRNA levels causes extreme variation in the expression of flowering genes, and disturbs flower determination and patterning (Margaritopoulou et al, 2016).…”

Brassinosteroid-induced de novo protein synthesis in Zea mays under salinity and bioinformatic approach for identification of heat shock proteins

“…Moreover, inhibitor of HSP90 ATPase activity-geldanamycin-suppressed BR-induced downregulation of key biosynthesis genes-CONSTITUTIVE PHOTHOMOR-PHOGENESIS AND DWARFISM (CPD) and DWARF4 in vivo (Shigeta et al 2014). HSP90 also assists nuclear localization of BRs signaling component-BIN2 (BRAS-SINOSTEROID INSENSITIVE 2) protein and geldanamycin treatment force BIN2 translocation to cytosol (Samakovli et al 2014). These point at involvement of HSPs into brassinosteroid signaling and regulation of BR-dependent genes.…”