D14–SCFD3-dependent degradation of D53 regulates strigolactone signalling

Abstract

Strigolactones (SLs) are a new class of carotenoid-derived phytohormones essential for developmental processes shaping plant architecture and interactions with parasitic weeds and symbiotic arbuscular mycorrhizal fungi. Despite the rapid progress in elucidating the SL biosynthetic pathway, the perception and signaling mechanisms of SL remain poorly understood. Here we show that DWARF53 (D53) acts as a repressor of SL signaling and SLs induce its degradation. We found that the rice d53 mutant, which produces an exaggerated number of tillers compared to wild type plants, is caused by a gain-of-function mutation and is insensitive to exogenous SL treatment. The D53 gene product shares predicted features with the class I Clp ATPase proteins and can form a complex with the α/β hydrolase protein DWARF14 (D14) and the F-box protein DWARF3 (D3), two previously identified signaling components potentially responsible for SL perception. We demonstrate that, in a D14- and D3-dependent manner, SLs induce D53 degradation by the proteasome and abrogate its activity in promoting axillary bud outgrowth. Our combined genetic and biochemical data reveal that D53 acts as a repressor of the SL signaling pathway, whose hormone-induced degradation represents a key molecular link between SL perception and responses.

Peptidyl-prolyl isomerization targets rice Aux/IAAs for proteasomal degradation during auxin signalling

“…Among these and other phytohormones, the activation of the signalling pathways of GA, jasmonic acid and strigolactone also utilize a derepression mechanism by the proteasomal degradation of specific repressors in a manner similar to that of auxin [44][45][46][47][48] . Interestingly, a GA-insensitive dwarf (gaid) mutant of wheat was characterized to be insensitive to exogenous GA, correlated to the elevated levels of the GA signalling repressor Rht/DELLA protein and a putative cyclophilin TaCYP20-2 protein.…”

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

“…GR24 can induce an interaction between D14 and D3, which has been shown in cells by yeast 2-hybrid analysis [25] and in extracts by pull-down assays [19,20]. To test whether GR24 directly stimulates an interaction between D14 and D3 in vitro, and to quantitatively analyze such an interaction, we used highly purified recombinant proteins in an AlphaScreen luminescence proximity assay.…”

“…Recent studies have identified the putative transcriptional repressor D53 [19,20] as well as the transcription factor BES1 as SCF D3 substrate targets in response to SL exposure and the D53 paralog SMAX1 in response to karrikin exposure. SLs induce association of D14 with D3/D53 and D3/BES1 complexes and promote SCF D3 -mediated degradation of D53 [19,20], BES1 [21], and D14 itself [22].…”

IPA1: a direct target of SL signaling

“…SL degrades the D53 protein in rice [4,5] and the related SMXL6, SMXL7 and SMXL8 proteins in Arabidopsis [1]. D53 directly prevents the transcriptional activation function of IPA1 (OsSPL14) in rice [2] and the related SPL3 and SPL17 proteins in wheat [8]; D53 prevents IPA1 upregulation of D53 gene expression in rice [2], and TaSPL3 upregulation of TaTB1 gene expression in wheat [8].…”

“…This interaction with D53 prevented the transcriptional activation activity of IPA1 in a dose-dependent manner (Figure 1). In rice, D53 is one of the only known transcriptional targets of SL [4,5], and D53 prevented IPA1 from upregulating D53 expression [2] ( Figure 1). By showing evidence of a mechanism via which SL signaling transcriptionally regulates downstream target genes, this work has enabled description of a continuous SL signaling pathway from perception to gene regulation ( Figure 1).…”