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

Abstract

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.

Ethylene Biosynthesis and Perception in Fruit

“…Wiersma et al (2007) observed that expression of MdACS3 increased 100-fold for 4 weeks before harvest and did not change upon ripening. Wang et al (2009) reported that MdACS3 expression preceded MdACS1 expression by at least 2 weeks. These results indicated that expression of MdACS3 was not affected by ethylene, and that this gene might be responsible for system 1 ethylene production in apple fruit.…”

“…Recently, Wang et al (2009) proposed that not only MdACS1, but also the MdACS3 allelic genotype, determines the differences in ethylene production among apple cultivars. Their group isolated three members of the MdACS3 gene family (a, b, c) and showed that transcription of MdACS3b and MdACS3c was prevented by insertion of transposon-like sequences in the 5' flanking region.…”

Molecular Characterization of Pear 1-Aminocyclopropane-1-Carboxylate Synthase Gene Preferentially Expressed in Leaves

“…As shown in Fig.3, these proteins obviously split into two subgroups. PpACS1, PcACS2b (El-Sharkawy et al, 2004), PcACS2a (El-Sharkawy et al, 2004, pPPACS2 (Itai et al, 1999), MdACS3a-2, MdACS3a-1, MdACS3c (Wang et al, 2009), PcACS3a, MdACS3b (Wang et al, 2009) and AtACS7 (Mayer et al, 1999) form one subgroup, while PbACS1B, pPPACS1 (Itai et al, 1999) and PcACS1b (El-Sharkawy et al, 2004) together with the Arabidopsis ACS8 are located in the second branch of the tree. These results suggest that the divergence could have occurred before the differentiation of the plants.…”

“…Lots of important ACC synthase genes have been isolated and characterized from the plant kingdom. For examples, ACS genes were identified in pear (Pyrus communis) (El-Sharkawy et al, 2004), Japanese pear (Pyrus pyrifolia) (Itai et al, 1999), apple (Rosenfield et al, 1996;Wang et al, 2009), peach (Mathooko et al, 2001;Tatsuki et al, 2006), pineapple (Cazzonelli et al, 1998;Botella et al, 2000;Trusov et al, 2006), plum (El-Sharkawy et al, 2008), cucumber (Mathooko et al, 1999), watermelon (Salman-Minkov et al, 2008), Arabidopsis (Rodrigues-Pousada et al, 1993;Mayer et al, 1999) , tomato (Nakatsuka et al, 1997), etc.…”

Characterization and expression profiles of MaACS and MaACO genes from mulberry (Morus alba L.)

“…The silencing of LeACS2 by vacuum-infiltration and the tobacco rattle virus (TRV)-based virus-induced gene silencing (VIGS) method also leads to a significant delay in the post-harvest ripening and senescence of tomato fruit (Xie et al, 2006). Moreover, null mutations of the MdACS1 and MdACS3 genes have shown no or very low expression levels of ripening-related genes and maintained firmness in apple fruit (Malus domestica) (Sunako et al, 1999;Wang et al, 2009).…”