E3 SUMO ligase AtSIZ1 positively regulates SLY1-mediated GA signaling and plant development
Gibberellins affect various plant development processes including germination, cell division and elongation, and flowering. A large number of studies have been carried out to address the molecular mechanisms that mediate gibberellin signaling effects on plant growth. However, such studies have been limited to DELLA protein degradation ; the regulatory mechanisms controlling how the stability and function of SLEEPY1 (SLY1), a protein that interacts with target DELLA proteins as components of the SCFSLY1 complex, is modulated at the post-translational level have not been addressed. Here, we show that the E3 SUMO ligase activity of AtSIZ1 regulates GA signaling in Arabidopsis by sumoylating SLY1. SLY1 was less abundant in siz1-2 mutants than in wild-type plants, but the DELLA protein RGA was more abundant in siz1-2 mutants than wild-type plants. SLY1 also accumulated to a high level in the SUMO protease mutant esd4. Transgenic sly1-13 mutants over-expressing SLY1 were phenotypically similar to wild-type plants; however, sly1-13 plants over-expressing a mutated mSLY1 protein (K122R, a mutation at the sumoylation site) retained the mutant dwarfing phenotype. Over-expression of SLY1 in sly1-13 mutants resulted in a return of RGA levels to wild-type levels, but RGA accumulated to high levels in mutants over-expressing mSLY1. RGA was clearly detected in Arabidopsis co-expressing AtSIZ1 and mSLY1, but not in plants co-expressing AtSIZ1 and SLY1. In addition, sumoylated SLY1 interacted with RGA and SLY1 sumoylation was significantly increased by GA. Taken together, our results indicate that, in Arabidopsis, AtSIZ1 positively controls GA signaling through SLY1 sumoylation.
Kim S; Park B; Kim D; Yeu S; Song S; Song J; Seo H
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