Destabilization of strigolactone receptor DWARF14 by binding of ligand and E3-ligase signaling effector DWARF3

Abstract

Strigolactones (SLs) are endogenous hormones and exuded signaling molecules in plant responses to low levels of mineral nutrients. Key mediators of the SL signaling pathway in rice include the α/β-fold hydrolase DWARF 14 (D14) and the F-box component DWARF 3 (D3) of the ubiquitin ligase SCF D3 that mediate ligand-dependent degradation of downstream signaling repressors. One perplexing feature is that D14 not only functions as the SL receptor but is also an active enzyme that slowly hydrolyzes diverse natural and synthetic SLs including GR24, preventing the crystallization of a binary complex of D14 with an intact SL as well as the ternary D14/SL/D3 complex. Here we overcome these barriers to derive a structural model of D14 bound to intact GR24 and identify the interface that is required for GR24-mediated D14-D3 interaction. The mode of GR24-mediated signaling, including ligand recognition, hydrolysis by D14, and ligand-mediated D14-D3 interaction, is conserved in structurally diverse SLs. More importantly, D14 is destabilized upon the binding of ligands and D3, thus revealing an unusual mechanism of SL recognition and signaling, in which the hormone, the receptor, and the downstream effectors are systematically destabilized during the signal transduction process.

Strigolactone Signaling in Arabidopsis Regulates Shoot Development by Targeting D53-Like SMXL Repressor Proteins for Ubiquitination and Degradation

“…This racemic mixture, known as rac-GR24, effectively stimulates SL signaling, but the enantiomer can stimulate the karrikin signaling pathway (Scaffidi et al, 2014). Therefore, purified GR24 stereoisomers with the configuration of 5DS or 4DO, designated as GR24 5DS and GR24 4DO , respectively, are used to stimulate SL signaling specifically (Scaffidi et al, 2014;Zhao et al, 2015).…”

“…The crystal structures of D14 proteins from rice, petunia (DAD2), and Arabidopsis ( D14) revealed an a/b-fold hydrolase with a large internal cavity capable of accommodating SLs and containing a canonical catalytic triad (Hamiaux et al, 2012;Bythell-Douglas et al, 2013;Kagiyama et al, 2013;Zhao et al, 2013Zhao et al, , 2015. The catalytic triad of DAD2/D14 is required for hydrolysis of SLs, which can trigger interaction between DAD2 and MAX2 in petunia and interaction between D14 and D3 in rice, as part of SCF-mediated signal transduction (Hamiaux et al, 2012;Smith and Waters, 2012;Jiang et al, 2013;Zhou et al, 2013;Zhao et al, 2014Zhao et al, , 2015. Furthermore, the crystal structure of D14 incubated with rac-GR24 revealed a derivative of the butenolide covalently attached to the active-site Ser residue .…”

LATERAL BRANCHING OXIDOREDUCTASE acts in the final stages of strigolactone biosynthesis in Arabidopsis

“…The active complex targets proteins for degradation, such as SMAX1-like proteins (SMXL6-SMXL8), and promotes expression of transcription factor genes, such as BRANCHED1, directly in buds (9)(10)(11)(12)(13). The active complex is unusual in that binding with strigolactone triggers destabilization and degradation of the D14 receptor and cleavage of the strigolactone compound (14)(15)(16). Negative feedback on some strigolactone biosynthesis genes has been observed in species, including pea and Arabidopsis (reviewed in ref.…”

From little things big things grow: karrikins and new directions in plant development

“…GR24 ent-5DS can substitute for karrikins in a range of KAI2-dependent assays, albeit with reduced sensitivity Waters et al 2015aWaters et al , 2015b. Likewise, D14 responds preferentially to GR24 5DS over GR24 ent-5DS (Nakamura et al 2013;Scaffidi et al 2014;Waters et al 2015b;Zhao et al 2015). The biological significance of KAI2 recognising non-naturallyconfigured strigolactones is unclear, but it does demonstrate that KAI2 and D14 exhibit distinct substrate preferences, which in part explains their functional differences.…”