Abstract
The reversible conjugation of the small ubiquitin-like modifier (SUMO) to protein substrates occurs as a posttranslational regulatory process in eukaryotic organisms. In Arabidopsis (Arabidopsis thaliana), several stress-responsive SUMO conjugations are mediated mainly by the SUMO E3 ligase SIZ1. In this study, we observed a phenotype of hypersensitivity to excess copper in the siz1-2 and siz1-3 mutants. Excess copper can stimulate the accumulation of SUMO1 conjugates in wild-type plants but not in the siz1 mutant. Copper accumulated to a higher level in the aerial parts of soil-grown plants in the siz1 mutant than in the wild type. A dramatic difference in copper distribution was also observed between siz1 and wild-type Arabidopsis treated with excess copper. As a result, the shoot-to-root ratio of copper concentration in siz1 is nearly twice as high as that in the wild type. We have found that copper-induced Sumoylation is involved in the gene regulation of metal transporters YELLOW STRIPE-LIKE 1 (YSL1) and YSL3, as the siz1 mutant is unable to down-regulate the expression of YSL1 and YSL3 under excess copper stress. The hypersensitivity to excess copper and anomalous distribution of copper observed in the siz1 mutant are greatly diminished in the siz1ysl3 double mutant and slightly in the siz1ysl1 double mutant. These data suggest that SIZ1-mediated sumoylation is involved specifically in copper homeostasis and tolerance in planta.
Highlights
The reversible conjugation of the small ubiquitin-like modifier (SUMO) to protein substrates occurs as a posttranslational regulatory process in eukaryotic organisms
Stress-responsive SUMO conjugation is mediated mainly by the SIZ1 SUMO E3 ligase in Arabidopsis
We found that siz1 mutants clearly display a shoot growth-retarded phenotype under conditions of excess Cu (Fig. 1; Supplemental Fig. S1)
Summary
The reversible conjugation of the small ubiquitin-like modifier (SUMO) to protein substrates occurs as a posttranslational regulatory process in eukaryotic organisms. Excess copper can stimulate the accumulation of SUMO1 conjugates in wild-type plants but not in the siz mutant. We have found that copper-induced Sumoylation is involved in the gene regulation of metal transporters YELLOW STRIPE-LIKE 1 (YSL1) and YSL3, as the siz mutant is unable to down-regulate the expression of YSL1 and YSL3 under excess copper stress. The hypersensitivity to excess copper and anomalous distribution of copper observed in the siz mutant are greatly diminished in the siz1ysl double mutant and slightly in the siz1ysl double mutant. These data suggest that SIZ1mediated sumoylation is involved in copper homeostasis and tolerance in planta. We were interested to find out whether excess Cu can induce sumoylation responses and, if yes, whether such responses play a role in the tolerance of excess Cu stress
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