Molecular characterization and expression of a cDNA encoding copper/zinc superoxide dismutase from cultured cells of cassava (Manihot esculenta Crantz).

A cDNA, mSOD1, encoding cytosolic copper/zinc superoxide dismutase (CuZnSOD) was cloned and characterized from cell cultures of cassava (Manihot esculenta Crantz) which produce a high yield of SOD. mSOD1 encodes a 152-amino acid polypeptide with a pI value of 5.84. Southern analysis using an mSOD1-specific probe indicated that a single copy of the mSOD1 gene is present in the cassava genome. The mSOD1 gene is highly expressed in cultured cells, as well as in intact stems and tuberous roots. It is expressed at a low level in leaves and petioles. Transcripts of mSOD1 were not detected in nontuberous roots. Transcriptional level of mSOD1 reaches a high level at stationary phase, and then sharply decreases during further culture. In excised cassava leaves, the mSOD1 gene responded to various stresses in different ways. The stresses tested included changes in temperature and exposure to stress-inducing chemicals. Levels of mSOD1 transcript increased dramatically a few hours after heat stress at 37 degrees C and showed a synergistic effect with wounding stress. Levels decreased in response to chilling stress at 4 degrees C and showed an antagonistic effect with wounding stress. The gene was induced by abscisic acid, ethephon, NaCl, sucrose, and methyl viologen. These results indicate that the mSOD1 gene is involved in the response to oxidative stress induced by environmental change.