Regulation of gibberellin signaling by E3 SUMO ligase SIZ1 in Arabidopsis thaliana

Abstract

Gibberellins affect various plant development processes including germination, cell division and elongation, and flowering. Here, I 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 wild-type plants. 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 (REPRESSOR of ga1-3) 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, my results indicate that AtSIZ1 positively controls GA signaling through SLY1 sumoylation.