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A dual positional specific lipoxygenase functions in the generation of flavor compounds during climacteric ripening of apple.

Schiller D, Contreras C, Vogt J, Dunemann F, Defilippi BG, Beaudry R, Schwab W - Hortic Res (2015)

Bottom Line: Site-directed mutagenesis of Gly567 to an alanine converted the dual positional specific LOX1:Md:1a to an enzyme with a high specificity for 9(S)-hydroperoxide formation.The high expression level of the corresponding MdLOX1a gene in stored apple fruit, the genetic association with a quantitative trait locus for fruit ester and the remarkable agreement in regio- and stereoselectivity of the LOX1:Md:1a reaction with the overall LOX activity found in mature apple fruits, suggest a major physiological function of LOX1:Md:1a during climacteric ripening of apples.While LOX1:Md:1c, LOX2:Md:2a and LOX2:Md:2b may contribute to aldehyde production in immature fruit upon cell disruption our results furnish additional evidence that LOX1:Md:1a probably regulates the availability of precursors for ester production in intact fruit tissue.

View Article: PubMed Central - PubMed

Affiliation: Biotechnology of Natural Products, Technische Universität München , Liesel-Beckmann-Str. 1, D-85354 Freising, Germany.

ABSTRACT
Lipoxygenase (LOX) is an important contributor to the formation of aroma-active C6 aldehydes in apple (Malus × domestica) fruit upon tissue disruption but little is known about its role in autonomously produced aroma volatiles from intact tissue. We explored the expression of 22 putative LOX genes in apple throughout ripening, but only six LOXs were expressed in a ripening-dependent manner. Recombinant LOX1:Md:1a, LOX1:Md:1c, LOX2:Md:2a and LOX2:Md:2b proteins showed 13/9-LOX, 9-LOX, 13/9-LOX and 13-LOX activity with linoleic acid, respectively. While products of LOX1:Md:1c and LOX2:Md:2b were S-configured, LOX1:Md:1a and LOX2:Md:2a formed 13(R)-hydroperoxides as major products. Site-directed mutagenesis of Gly567 to an alanine converted the dual positional specific LOX1:Md:1a to an enzyme with a high specificity for 9(S)-hydroperoxide formation. The high expression level of the corresponding MdLOX1a gene in stored apple fruit, the genetic association with a quantitative trait locus for fruit ester and the remarkable agreement in regio- and stereoselectivity of the LOX1:Md:1a reaction with the overall LOX activity found in mature apple fruits, suggest a major physiological function of LOX1:Md:1a during climacteric ripening of apples. While LOX1:Md:1c, LOX2:Md:2a and LOX2:Md:2b may contribute to aldehyde production in immature fruit upon cell disruption our results furnish additional evidence that LOX1:Md:1a probably regulates the availability of precursors for ester production in intact fruit tissue.

No MeSH data available.


Related in: MedlinePlus

The LOX pathway. The dioxygenation of PUFAs by 9- and 13-LOX activity forms precursors for important phytooxylipins with functions in plant defense, wound signaling, senescence and fruit ripening. The formation of fruit esters from 13-hydroperoxide occurs by the HPL pathway and the action of AAT. AAT, alcohol acyl-CoA transferase; ADH, alcohol dehydrogenase; AOS, allene oxid synthase; DES, divinyl ether synthase; HPL, hydroperoxide lyase; POX, peroxygenase, PUFA, polyunsaturated fatty acid. Adapted from Feussner and Wasternack.13
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fig1: The LOX pathway. The dioxygenation of PUFAs by 9- and 13-LOX activity forms precursors for important phytooxylipins with functions in plant defense, wound signaling, senescence and fruit ripening. The formation of fruit esters from 13-hydroperoxide occurs by the HPL pathway and the action of AAT. AAT, alcohol acyl-CoA transferase; ADH, alcohol dehydrogenase; AOS, allene oxid synthase; DES, divinyl ether synthase; HPL, hydroperoxide lyase; POX, peroxygenase, PUFA, polyunsaturated fatty acid. Adapted from Feussner and Wasternack.13

Mentions: LOX (linoleate oxygen oxidoreductase, EC 1.13.11.12) are non-heme iron-containing dioxygenases. They catalyse the regio- and stereospecific introduction of molecular dioxygen into polyunsaturated fatty acids, containing a Z,Z-1,4-pentadiene system such as LA and LnA to form hydroperoxy octadecadienoic acid (HpODE) and hydroperoxy octadecatrienoic acid, respectively.11 Plant LOX are classified according to the position of oxygenation in the carbon backbone of LA.12 This occurs either at carbon atom 9 (9-LOX) or 13 (13-LOX), forming the corresponding hydroperoxy derivatives, respectively (Figure 1). However, LOX enzymes are not perfectly specific and biocatalysts that produce more than 10% of the alternative regio-isomer are called dual positional specific LOX.14 Both 9- and 13-hydroperoxides can be catabolized to aroma-active volatile aldehydes by hydroperoxide lyase. However, only 13-LOX activity contributes to the apple aroma due to the formation of precursors of C6 volatile compounds.15 Alternatively, LOX genes are classified based on comparison of LOX primary structures.13 Most plant LOX share high sequence similarity of about 70% and are therefore grouped into the so-called type-1 LOX class. Members of the type-2 LOX class show only moderate sequence similarity but exhibit a putative chloroplast transit peptide.12 TomloxC, a chloroplast-targeted LOX from tomato, has been identified as key LOX specifically involved in the generation of fatty acid-derived C6 aldehydes and alcohols upon tissue disruption.16


A dual positional specific lipoxygenase functions in the generation of flavor compounds during climacteric ripening of apple.

Schiller D, Contreras C, Vogt J, Dunemann F, Defilippi BG, Beaudry R, Schwab W - Hortic Res (2015)

The LOX pathway. The dioxygenation of PUFAs by 9- and 13-LOX activity forms precursors for important phytooxylipins with functions in plant defense, wound signaling, senescence and fruit ripening. The formation of fruit esters from 13-hydroperoxide occurs by the HPL pathway and the action of AAT. AAT, alcohol acyl-CoA transferase; ADH, alcohol dehydrogenase; AOS, allene oxid synthase; DES, divinyl ether synthase; HPL, hydroperoxide lyase; POX, peroxygenase, PUFA, polyunsaturated fatty acid. Adapted from Feussner and Wasternack.13
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4595979&req=5

fig1: The LOX pathway. The dioxygenation of PUFAs by 9- and 13-LOX activity forms precursors for important phytooxylipins with functions in plant defense, wound signaling, senescence and fruit ripening. The formation of fruit esters from 13-hydroperoxide occurs by the HPL pathway and the action of AAT. AAT, alcohol acyl-CoA transferase; ADH, alcohol dehydrogenase; AOS, allene oxid synthase; DES, divinyl ether synthase; HPL, hydroperoxide lyase; POX, peroxygenase, PUFA, polyunsaturated fatty acid. Adapted from Feussner and Wasternack.13
Mentions: LOX (linoleate oxygen oxidoreductase, EC 1.13.11.12) are non-heme iron-containing dioxygenases. They catalyse the regio- and stereospecific introduction of molecular dioxygen into polyunsaturated fatty acids, containing a Z,Z-1,4-pentadiene system such as LA and LnA to form hydroperoxy octadecadienoic acid (HpODE) and hydroperoxy octadecatrienoic acid, respectively.11 Plant LOX are classified according to the position of oxygenation in the carbon backbone of LA.12 This occurs either at carbon atom 9 (9-LOX) or 13 (13-LOX), forming the corresponding hydroperoxy derivatives, respectively (Figure 1). However, LOX enzymes are not perfectly specific and biocatalysts that produce more than 10% of the alternative regio-isomer are called dual positional specific LOX.14 Both 9- and 13-hydroperoxides can be catabolized to aroma-active volatile aldehydes by hydroperoxide lyase. However, only 13-LOX activity contributes to the apple aroma due to the formation of precursors of C6 volatile compounds.15 Alternatively, LOX genes are classified based on comparison of LOX primary structures.13 Most plant LOX share high sequence similarity of about 70% and are therefore grouped into the so-called type-1 LOX class. Members of the type-2 LOX class show only moderate sequence similarity but exhibit a putative chloroplast transit peptide.12 TomloxC, a chloroplast-targeted LOX from tomato, has been identified as key LOX specifically involved in the generation of fatty acid-derived C6 aldehydes and alcohols upon tissue disruption.16

Bottom Line: Site-directed mutagenesis of Gly567 to an alanine converted the dual positional specific LOX1:Md:1a to an enzyme with a high specificity for 9(S)-hydroperoxide formation.The high expression level of the corresponding MdLOX1a gene in stored apple fruit, the genetic association with a quantitative trait locus for fruit ester and the remarkable agreement in regio- and stereoselectivity of the LOX1:Md:1a reaction with the overall LOX activity found in mature apple fruits, suggest a major physiological function of LOX1:Md:1a during climacteric ripening of apples.While LOX1:Md:1c, LOX2:Md:2a and LOX2:Md:2b may contribute to aldehyde production in immature fruit upon cell disruption our results furnish additional evidence that LOX1:Md:1a probably regulates the availability of precursors for ester production in intact fruit tissue.

View Article: PubMed Central - PubMed

Affiliation: Biotechnology of Natural Products, Technische Universität München , Liesel-Beckmann-Str. 1, D-85354 Freising, Germany.

ABSTRACT
Lipoxygenase (LOX) is an important contributor to the formation of aroma-active C6 aldehydes in apple (Malus × domestica) fruit upon tissue disruption but little is known about its role in autonomously produced aroma volatiles from intact tissue. We explored the expression of 22 putative LOX genes in apple throughout ripening, but only six LOXs were expressed in a ripening-dependent manner. Recombinant LOX1:Md:1a, LOX1:Md:1c, LOX2:Md:2a and LOX2:Md:2b proteins showed 13/9-LOX, 9-LOX, 13/9-LOX and 13-LOX activity with linoleic acid, respectively. While products of LOX1:Md:1c and LOX2:Md:2b were S-configured, LOX1:Md:1a and LOX2:Md:2a formed 13(R)-hydroperoxides as major products. Site-directed mutagenesis of Gly567 to an alanine converted the dual positional specific LOX1:Md:1a to an enzyme with a high specificity for 9(S)-hydroperoxide formation. The high expression level of the corresponding MdLOX1a gene in stored apple fruit, the genetic association with a quantitative trait locus for fruit ester and the remarkable agreement in regio- and stereoselectivity of the LOX1:Md:1a reaction with the overall LOX activity found in mature apple fruits, suggest a major physiological function of LOX1:Md:1a during climacteric ripening of apples. While LOX1:Md:1c, LOX2:Md:2a and LOX2:Md:2b may contribute to aldehyde production in immature fruit upon cell disruption our results furnish additional evidence that LOX1:Md:1a probably regulates the availability of precursors for ester production in intact fruit tissue.

No MeSH data available.


Related in: MedlinePlus