IDENTIFICATION AND CHARACTERIZATION OF A FULL-LENGTH CDNA-ENCODING FOR AN AUXIN-INDUCED 1-AMINOCYCLOPROPANE-1-CARBOXYLATE SYNTHASE FROM ETIOLATED MUNG BEAN HYPOCOTYL SEGMENTS AND EXPRESSION OF ITS MESSENGER-RNA IN RESPONSE TO INDOLE-3-ACETIC-ACID

1-Aminocyclopropane-1-carboxylate (ACC) synthase (EC 4.4.1.14) is the key regulatory enzyme in the ethylene biosynthetic pathway. The identification and characterization of a full-length cDNA (pAIM-1) 1941 bp in length for indole-3-acetic acid (IAA)-induced ACC synthase is described in this paper. The pAIM-1 clone has an 87 bp leader and a 402 bp trailing sequence. The open reading frame is 1452 bp long encoding for a 54.6 kDa polypeptide (484 amino acids) which has a calculated isoelectric point of 6.0. In vitro transcription and translation experiments support the calculated molecular weight and show that the enzyme does not undergo processing. Eleven of the twelve amino acid residues which are conserved in aminotransferases are found in pAIM-1. The sequence for pMAC-1 which is one of the 5 genes we have identified in mung bean is contained in pAIM-1. pAIM-1 shares between 52 to 65% homology with previously reported sequences for ACC synthase at the protein level. There is little detectable pAIM-1 message found in untreated mung bean tissues; however, expression is apparent within 30 min following the addition of 10 muM IAA reaching a peak after approximately 5 h with a slight decrease in message after 12 h. These changes in message correlate with changes in ACC levels found in these tissues following treatment with 10 muM IAA.