Cloning of an auxin-responsive 1-aminocyclopropane-1-carboxylate synthase gene (CMe-ACS2) from melon and the expression of ACS genes in etiolated melon seedlings and melon fruits

Two cDNA fragments (pCMe-ACS2 and 3) encoding auxin-responsive 1-aminocyclo propane-1-carboxylate synthase (ACS; EC.4.4.1.14) have been isolated from m elon, and the expression patterns of the genes in etiolated melon seedlings and melon fruit have been determined by RT-PCR analysis. The deduced amino acid sequences of pCMe-ACS2 and 3 were homologous to those of AT-ACS6 and 4, which were auxin-responsive ACS genes of Arabidopsis. Both CMe-ACS2 and 3 were auxin-responsive A CS genes and their expressions in roots and hypoc otyls were induced by treatment with indole acetic acid (IAA, 100 muM). The mRNA level of CMe-ACS2 in the fruit increased after pollination. Those of both Cr CMe-ACS2 and 3 temporarily increased in the mesocarp tissues at the preclimacteric stage (from day 3 to day 5 after harvest) during ripening, while that of CMe-ACS3 was lower than that of CMe-ACS2. The increase in the mRNA level of CMe-ACS1 (wound- and ripening-induced gene, T. Miki, M. Yama moto, N. Nakagawa, O. Ogura. H. Mori, H. Imaseki, T. Sate, Nucleotide seque nce of a cDNA for 1-aminocyclopropane-1-carboxylate synthase from melon fru its, Plant Physiol. 107 (1995) 297-298.) in the mesocarp tissue was not obs erved until 5 days after harvest. A genomic DNA encoding CMe-ACS2 was isola ted and its nucleotide sequence was determined. Nucleotide sequences resemb ling the auxin-responsive elements (AuxRE) D1 and D4 (the TGTCTC element) i n the GH3 gene from soybean, and the auxin-responsive domain (AuxRD) B in P S-IAA4/5 from pea were found in the 5'-flanking region of the CMe-ACS2 gene . (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.