Effect of Cu content on the activity of Cu/ZnSOD1 in the Arabidopsis SUMO E3 ligase siz1 mutant

Abstract

In a previous study, we found copper (Cu) accumulated to a higher level in the aerial parts of soil-grown plants of the SUMO E3 ligase siz1 mutant than in those of the wild type. Here, we found that all superoxide dismutase (SOD) isoforms, such as FeSOD, MnSOD and different types of Cu/ZnSOD, were more active in the siz1 mutant than in the wild type under normal growth conditions. We further examined the expression and enzymatic activity of Cu/ZnSOD1 (CSD1) in shoots of the siz1 mutant under excess Cu. Shoot CSD1 protein level and activity were reduced in siz1 with excess Cu but induced in the wild type. SIZ1-dependent SUMOylation may be involved in maintaining CSD1 protein stability or repelling a feedback regulation under Cu stress.

Figure 1

Expression of superoxide dismutase (SOD) enzymes. (A) SOD isozyme activity. Activities of different SOD enzymes in leaves of the wild type (WT) and SUMO E3 ligase mutant siz1 (siz1–2 and siz1–3) plants grown for 3 weeks and treated with 1/2 MS solution (C) or 1/2 MS + 25 µM CuSO₄ (Cu) for 5.5 h; SOD isoforms are indicated. Total proteins (50 µg) were separated on 10% native polyacrylamide gels and stained for total SOD activity. (B) Quantitative RT-PCR analysis of mRNA expression of Cu/ZnSOD1 (CSD1) in shoot and root tissues. Twelve-day-old WT and siz1–2 plants were treated with 25 µM CuSO₄ for 1 d. Y-axis represents expression relative to that of ACT2. Means and error bars were calculated from 6 samples of two biological repeats. *p < 0.01 compared with 1/2 MS. (C) Protein gel blot analysis of CSD1 protein level in the wild type and siz1–2 (siz1) with or without Cu treatment.