Ethylene is a plant hormone. It regulates many aspects of plant growth and development. Production of ethylene in higher plants can be induced by environmental stresses such as low temperature chilling. However, little information is available about the molecular mechanism of the induction of ethylene biosynthesis. It has been established that ethylene is synthesized via the following pathway : methionine → S-adenosyl-L- methionine (SAM) → 1-aminocyclopropane- 1-carboxylic acid (ACC) → ethylene (Adams and Yang 1979). These reactions are catalyzed by two key enzymes, ACC synthase and ACC oxidase. The formation of ACC is the rate-limiting step in this pathway. The study of the regulation of gene expression of ACC synthase will elucidate the mechanism and regulation of ethylene biosynthes...[ Read more ]

Ethylene is a plant hormone. It regulates many aspects of plant growth and development. Production of ethylene in higher plants can be induced by environmental stresses such as low temperature chilling. However, little information is available about the molecular mechanism of the induction of ethylene biosynthesis. It has been established that ethylene is synthesized via the following pathway : methionine → S-adenosyl-L- methionine (SAM) → 1-aminocyclopropane- 1-carboxylic acid (ACC) → ethylene (Adams and Yang 1979). These reactions are catalyzed by two key enzymes, ACC synthase and ACC oxidase. The formation of ACC is the rate-limiting step in this pathway. The study of the regulation of gene expression of ACC synthase will elucidate the mechanism and regulation of ethylene biosynthesis at molecular level. Two ACC synthase genes, CS-ACS1 and CS-ACS2, were isolated by RT-PCR using the total RNA purified from citrus peel (Citrus sinensis, Osbeck) as template and degenerated oligonucleotides synthesized based on the highly conserved regions of the ACC synthase amino acid sequence. Northern blot analysis showed that the expression of CS-ACS1 in citrus (Citrus sinensis, Osbeck) peel was chilling-inducible, whereas CS-ACS2 was chilling-repressable. The genomic DNA sequence of CS-ACS1 has been isolated. The 3,289 bp nucleotide sequence covers the open reading frame of CS-ACS1. There are four exons and three introns found in CS-ACS1. The open reading frame of CS-ACSl gene encodes a polypeptide of 483 amino acids. Sequence alignment with other ACC synthase genes retrieved from the GenBank showed that the CS-ACSl is evolutional closely related to both Pelargonium hortorum ACS gene and another chilling- inducible tobacco ACS gene. Our results also showed that the ethylene prodction was induced by chilling treatment in both detached kumquat (Fortunella margarita, Swingle) leaves and citrus (Citrus sinensis, Osbeck) fruit. Moreover, a rise in ACC level in citrus peel was also observed upon chilling treatment.