The ACC Synthase Genes and Polypeptides

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Ethylene is an unique plant signaling molecule. The hydrocarbon gas, known as the fruit ripening hormone, controls many aspects of plant growth and development. It is biosynthesized from methionine via a three-step enzymatic process: SAM ACC ACC Methionine SAM ACC C2H4. Synthase synthase oxidaseIts synthesis is highly regulated. Experimental evidence accumulated over the last 10 years indicates that one of the key enzymes in the ethylene biosynthetic pathway, 1-aminocyclopropane-1-carboxylic acid (ACC) synthase (ACS), is encoded by a highly divergent multigene family in various mono- and dicotyledonous plants. The completion of the Arabidopsis genome sequence reveals the presence of 10 putative ACS genes (ACS2, 4-12) and two pseudogenes (ACS1, ACS3). Expression studies reveal that the family members are differentially regulated by various inducers and developmental stages Studies on the regulation of the ACS genes in Arabidopsis are proposed here to gain insight into the details of the signaling machinery involved primarily in the regulation of the ACS gene by auxin and ethylene. Further studies are proposed to obtain knowledge regarding the structure and the biochemical properties of the ACS isoenzymes. The proposed molecular and biochemical experimental approaches attempt to answer the following question: why are there 10 ACC synthase isoenzymes in Arabidopsis for the synthesis of the ethylene precursor ACC? While all of them have the same biochemical function, the question arises whether they have distinct or redundant biological function. The findings have the potential to allow a fundamental understanding of the role of multigene families in plants, a hallmark finding of the Arabidopsis Genome Sequencing project.