Molecular cloning of an ozone-induced 1-aminocyclopropane-1-carboxylate synthase cDNA and its relationship with a loss of rbcS in potato (Solanum tuberosum L.) plants

Acute or chronic exposure of potato plants to ozone (O₃) induces ethylene production. We isolated a 1586 bp cDNA (pOIP-1) encoding 1-aminocyclopropane-1-carboxylate (ACC) synthase from a cDNA library constructed with mRNA extracted from O₃-treated leaves. The clone has a 1365 bp open reading frame and a 221 bp trailing sequence. The active site found in all ACC synthases and 11 of the 12 amino acid residues conserved in aminotransferases are found in pOIP-1. Northern analysis showed that the mRNA encoding ACC synthase was detectable 1 h after the onset of O₃ exposure, and the message increased over time as did ethylene production. Concurrent with the increased ACC synthase mRNA was a decrease in the message for the Rubisco small subunit (rbcS) with no change in the large subunit (rbcL). When the plants were treated with aminooxyacetic acid (AOA), both ethylene production and level of ACC synthase transcript were inhibited. The decline in rbcS was also inhibited by AOA suggesting a correlation between ethylene production and loss of rbcS. Based on nuclear run-on studies it appears that the increase in ACC synthase mRNA may result from O₃-induced transcriptional activity.