Expression of α-Farnesene Synthase AFS1 and 3-Hydroxy-3-methylglutaryl-coenzyme A Reductase HMG2 and HMG3 in Relation to α-Farnesene and Conjugated Trienols in `Granny Smith' Apples Heat or 1-MCP Treated to Prevent Superficial Scald

Abstract

<jats:p>Untreated control, 1-methylcyclopropene (1-MCP)-treated, and heated fruit of the superficial scald-susceptible `Granny Smith' cultivar of apple [<jats:italic>Malus sylvestris</jats:italic> (L.) Mill. var. <jats:italic>domestica</jats:italic> (Borkh.) Mansf.] were compared with respect to scald incidence, internal ethylene concentration (IEC), α-farnesene metabolism, expression of the genes <jats:italic>AFS1</jats:italic>, which encodes α-farnesene synthase, the final, rate-limiting enzyme in the α-farnesene biosynthetic pathway, and <jats:italic>HMG2</jats:italic> and <jats:italic>HMG3</jats:italic>, which encode isozymes of 3-hydroxy-3-methylglutaryl-coenzyme A reductase, the proposed rate-limiting enzyme in the mevalonate pathway of isoprenoid synthesis. The incidence of scald in untreated `Granny Smith' apples after 16 weeks at 0 °C plus 1 week at 20 °C was 100%; 1-MCP treatment prevented scald development, whereas heat treatment delayed and reduced scald development. 1-MCP also inhibited both α-farnesene and IEC, suggesting that ethylene induces transcription of key genes involved in α-farnesene biosynthesis. Heat treatment reduced levels of α-farnesene and and its oxidation products, conjugated trienols (CTols), but not to the extent of 1-MCP. Internal ethylene concentrations in heated apples did not differ from those in the controls. In both control and heated fruit, a sharp increase in <jats:italic>AFS1</jats:italic> mRNA during the first 4 weeks of storage preceded an increase in α-farnesene and a subsequent increase in CTols. <jats:italic>AFS1</jats:italic> transcript was absent from 1-MCP-treated apples for the first 10 weeks of storage, and even at 16 weeks was lower than in heated and untreated control fruit. Levels of the <jats:italic>HMG2</jats:italic> and <jats:italic>HMG3</jats:italic> transcripts varied during storage and among treatments, and were not correlated with the incidence of scald. <jats:italic>HMG2</jats:italic> mRNA transcript accumulation was low at harvest and increased in abundance during storage in all treatments, with the greatest increase occurring in 1-MCP-treated fruit. In contrast, <jats:italic>HMG3</jats:italic> transcript was constitutively present at all storage times, although it too was slightly more abundant in 1-MCP-treated fruit.</jats:p>

A simple pretreatment with low O2 to alleviate superficial scald in Granny Smith apples

“…The effect of AA in inhibiting ethylene production has been shown in several other fruits, including grape, tomato, mango, avocado and banana 17. It is well known that ethylene mediates the synthesis of α‐farnesene, leading to scald symptoms,5, 6 and that application of 1‐MCP, an ethylene action inhibitor, prevents scald development in apples 3, 7–12. Also in our research, application of 1‐MCP was the most effective at reducing ethylene production, leading to lower scald development.…”

“…The development of scald is caused by autoxidation products of α‐farnesene, identified as conjugated trienes and 6‐methyl‐5‐hepten‐2‐one, in apple skin 4. Several studies have shown that the synthesis of α‐farnesene is mediated by ethylene,5, 6 and in recent years many studies have demonstrated that the ethylene action inhibitor 1‐methylcyclopropene (1‐MCP) is very powerful at preventing scald in apples, which again confirms that ethylene is the main inducer of scald development 3, 7–12…”

Target metabolite and gene transcription profiling during the development of superficial scald in apple (Malus x domestica Borkh)

“…According to other references [[16],[19],[20],[33]] α-farnesene was linearly accumulated after the first month of cold storage and in particular during the first period of room temperature shelf life, with a clear increase from the T1 +1 to T1 +8 stages, after which a more constant profile was observed during T2 shelf life (Figure 4B). The burst in this volatile was positively correlated with the activation and transcription dynamics of MdAFS1 , the gene designated to encoding the last step of the α-farnesene synthesis (Figure 4A).…”

An insight into the role of fruit maturity at harvest on superficial scald development in ‘Beurré D’Anjou’ pear

“…In apples, ethylene is known to play a key role in the development of superficial scald since this hormone is involved in the synthesis of ␣-farnesene by regulating gene expression of hydroxymethylglutaryl-CoA reductase (HMGR) and/or ␣-farnesene synthase (Ju and Curry, 2000). Accordingly, scaldsusceptible pears and apples typically exhibit higher rate of ␣-farnesene (AF) than resistant fruit, shortly after they are placed in low temperature storage (Huelin and Coggiola, 1970;Whitaker et al, 1997;Lurie et al, 2005;Gapper et al, 2006;Giné Bordonaba et al, 2013).…”