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DEVELOPMENT AND HORMONE ACTION

Null Mutation of the MdACS3 Gene, Coding for a Ripening-Specific 1-Aminocyclopropane-1-Carboxylate Synthase, Leads to Long Shelf Life in Apple Fruit^1,[W],[OA]

Laboratory of Plant Breeding and Genetics, Faculty of Agriculture and Life Science, Hirosaki University, Hirosaki 036–8561, Japan (A.W., J.Y., H.K., A.K., T.H.); National Institute of Agrobiological Science, Tsukuba 305–8602, Japan (Y.W.); Aomori Prefectual Industrial Technology Research Center, Hirosaki 036–8363, Japan (Y.H., M.I.); and Laboratory of Fruit Cell and Molecular Breeding, College of Agronomy and Bio-tech, China Agricultural University, Beijing 100193, China (T.L.)

Expression of MdACS1, coding for 1-aminocyclopropane-1-carboxylate synthase (ACS), parallels the level of ethylene production in ripening apple (Malus domestica) fruit. Here we show that expression of another ripening-specific ACS gene (MdACS3) precedes the initiation of MdACS1 expression by approximately 3 weeks; MdACS3 expression then gradually decreases as MdACS1 expression increases. Because MdACS3 expression continues in ripening fruit treated with 1-methylcyclopropene, its transcription appears to be regulated by a negative feedback mechanism. Three genes in the MdACS3 family (a, b, and c) were isolated from a genomic library, but two of them (MdACS3b and MdACS3c) possess a 333-bp transposon-like insertion in their 5' flanking region that may prevent transcription of these genes during ripening. A single nucleotide polymorphism in the coding region of MdACS3a results in an amino acid substitution (glycine-289 valine) in the active site that inactivates the enzyme. Furthermore, another null allele of MdACS3a, Mdacs3a, showing no ability to be transcribed, was found by DNA sequencing. Apple cultivars homozygous or heterozygous for both null allelotypes showed no or very low expression of ripening-related genes and maintained fruit firmness. These results suggest that MdACS3a plays a crucial role in regulation of fruit ripening in apple, and is a possible determinant of ethylene production and shelf life in apple fruit.

² These authors contributed equally to the article.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Takeo Harada (tharada{at}cc.hirosaki-u.ac.jp).

^[W] The online version of this article contains Web-only data.

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www.plantphysiol.org/cgi/doi/10.1104/pp.109.135822

^* Corresponding author; e-mail tharada{at}cc.hirosaki-u.ac.jp.

Received January 16, 2009; accepted June 28, 2009; published July 8, 2009.