Expression and characterization of monocot rice cytosolic CuZnSOD protein in dicot Arabidopsis

Cytosolic CuZnSOD removes deleterious superoxides from plant cells. In orde r to understand its function better, we sought to express a monocot CuZnSOD gene in transgenic Arabidopsis. We constructed a transgene usingthe CaMV 35 S promoter to express a rice cytosolic CuZnSOD gene in Arabidopsis and gene rated over 200 transformants. A 16 kD polypeptide, the same size as the nat ive rice CuZnSOD polypeptide, was detected inthe transgenic Arabidopsis. In terestingly, two forms of riceCuZnSOD, rSODI and rSODII, having the same di meric size, were detectedin the transgenic plants. rSODII protein was relat ively abundant but hadlow specific activity. In contrast, rSODI protein was relatively rareand had high specific activity. Inter-conversion of rSODI a nd rSODIIcould be achieved by the addition and removal of copper ions into the purifiedrecombinant SOD and to the leaf extract of transgenic plants. O uranalysis indicates that rSODI most likely corresponds to native riceCuZnS OD that has incorporated the Cu and Zn ions required for fullactivity, wher eas the less active rSODII form may not have properlyincorporated the neces sary copper ions.