ASC4, a Primary Indoleacetic Acid-responsive Gene Encoding 1-Aminocyclopropane-1-carboxylate Synthase in Arabidopsis thaliana

Abstract

1-Aminocyclopropane-1-carboxylic acid (ACC) synthase is the key regulatory enzyme in the biosynthetic pathway of the plant hormone ethylene. The enzyme is encoded by a divergent multigene family in Arabidopsis thaliana, comprising at least five genes, ACS1-5 (Liang, X., Abel, S., Keller, J.A., Shen,N. N.F., and Theologis, A. (1992) Poc. Natl. Acad. Sci. U.S.A. 89, 11046-11050). In etiolated seedlings, ACS4 is specifically induced by indoleacetic acid (IAA). The response to IAA is rapid (within 25 min) and insensitive to protein synthesis inhibition, suggesting that the ACS4 gene expression is a primary response to IAA. The ACS4 mRNA accumulation displays a biphasic dose-response curve which is optimal at 10 microM of IAA. However, IAA concentrations as low as 100 microM are sufficient to enhance the basal level of ACS4 mRNA. The expression of ACS4 is defective in the Arabidopsis auxin-resistant mutant lines axr1-12, axr2-1, and aux1-7. ACS4 mRNA levels are severely reduced in axr1-12 and axr2-1 but are only 1.5-fold lower in aux1-7. IAA inducibility is abolished in axr2-1. The ACS4 gene was isolated and structurally characterized. The promoter contains four sequence motifs reminiscent of functionally defined auxin-responsive cis-elements in the early auxin-inducible genes PS-IAA4/5 from pea and GH3 from soybean. Conceptual translation of the coding region predicts a protein with a molecular mass of 53,795 Da and a theoretical isoelectric point of 8.2. The ACS4 polypeptide contains the 11 invariant amino acid residues conserved between aminotransferases and ACC synthases from various plant species. An ACS4 cDNA was generated by reverse transcriptase-polymerase chain reaction, and the authenticity was confirmed by expression of ACC synthase activity in Escherichia coli.

SAUR36, a SMALL AUXIN UP RNA Gene, Is Involved in the Promotion of Leaf Senescence in Arabidopsis

“…A GFP fusion protein confirms that the SAUR36 protein is targeted to the nucleus (Narsai et al, 2011). Auxin can activate the 1-aminocyclopropane-1-carboxylate biosynthetic step to stimulate ethylene production, which in turn promotes senescence (Abel et al, 1995). Whether this nuclear protein functions through or is independent of ethylene has yet to be investigated.…”

Isolation and characterization of a copalyl diphosphate synthase gene promoter from Salvia miltiorrhiza

“…Generally speaking, a putative biphasic or positive feedback loop response was observed for the two analyzed plant hormones [61].…”

The role of PnACO1 in light- and IAA-regulated flower inhibition in Pharbitis nil

“…Therefore, it seems that auxin's inhibiting effect on P. nil flowering is achieved by an increased level of ethylene. It could be so, because it was proved that auxins induce the expression of some ACC synthases (Arteca and Arteca 1999;Frankowski et al 2009;Kęsy et al 2010;Tian et al 2002;Tsuchisaka and Theologis 2004a), while the level of these genes' expression correlates with the level of ethylene production (Abel et al 1995;Kęsy et al 2008;Overmyer et al 2000;Smith and Arteca 2000;Tian et al 2002;Tsuchisaka and Theologis 2004b).…”