Short-chain esters contribute to the blend of volatiles that define the strawberry aroma. The last step in their biosynthesis involves an alcohol acyltransferase that catalyses the esterification of ...an acyl moiety of acyl-CoA with an alcohol. This study identified a novel strawberry alcohol acyltransferase gene (FaAAT2) whose expression pattern during fruit receptacle growth and ripening is in accordance with the production of esters throughout strawberry fruit ripening. The full-length FaAAT2 cDNA was cloned and expressed in Escherichia coli and its activity was analysed with acyl-CoA and alcohol substrates. The semi-purified FaAAT2 enzyme had activity with C1–C8 straight-chain alcohols and aromatic alcohols in the presence of acetyl-CoA. Cinnamyl alcohol was the most efficient acyl acceptor. When FaAAT2 expression was transiently downregulated in the fruit receptacle by agroinfiltration, the volatile ester production was significantly reduced in strawberry fruit. The results suggest that FaAAT2 plays a significant role in the production of esters that contribute to the final strawberry fruit flavour.
Plant phenolics have drawn increasing attention due to their potential nutritional benefits. Although the basic reactions of the phenolics biosynthetic pathways in plants have been intensively ...analyzed, the regulation of their accumulation and flux through the pathway is not that well established. The aim of this study was to use a strawberry (Fragaria × ananassa) microarray to investigate gene expression patterns associated with the accumulation of phenylpropanoids, flavonoids, and anthocyanins in strawberry fruit. An examination of the transcriptome, coupled with metabolite profiling data from different commercial varieties, was undertaken to identify genes whose expression correlated with altered phenolics composition. Seventeen comparative microarray analyses revealed 15 genes that were differentially (more than 200-fold) expressed in phenolics-rich versus phenolics-poor varieties. The results were validated by heterologous expression of the peroxidase FaPRX27 gene, which showed the highest altered expression level (more than 900-fold). The encoded protein was functionally characterized and is assumed to be involved in lignin formation during strawberry fruit ripening. Quantitative trait locus analysis indicated that the genomic region of FaPRX27 is associated with the fruit color trait. Down-regulation of the CHALCONE SYNTHASE gene and concomitant induction of FaPRX27 expression diverted the flux from anthocyanins to lignin. The results highlight the competition of the different phenolics pathways for their common precursors. The list of the 15 candidates provides new genes that are likely to impact polyphenol accumulation in strawberry fruit and could be used to develop molecular markers to select phenolics-rich germplasm.
Strawberry (Fragaria × ananassa) is a fruit crop with a distinct biphasic flavonoid biosynthesis. Whereas, in the immature receptacle, high levels of proanthocyanidins accumulate, which are ...associated with herbivore deterrence and pathogen defense, the prominent color-giving anthocyanins are primarily produced in ripe ‘fruits’ helping to attract herbivores for seed dispersal.
Here, constitutive experimental down-regulation of one branch of proanthocyanidin biosynthesis was performed.
As a result, the proportion of epicatechin monomeric units within the proanthocyanidin polymer chains was reduced, but this was not the case for the epicatechin starter unit. Shortened chain lengths of proanthocyanidins were also observed. All enzymatic activities for the production of color-giving anthocyanins were already present in unripe fruits at levels allowing a striking red anthocyanin phenotype in unripe fruits of the RNAi silencing lines. An immediately recognizable phenotype was also observed for the stigmata of flowers, which is another epicatechin-forming tissue.
Thus, the down-regulation of anthocyanidin reductase (ANR) induced a redirection of the proanthocyanidin pathway, leading to premature and ectopic anthocyanin biosynthesis via enzymatic glycosylation as the alternative pathway. This redirection is also seen in flavonol biosynthesis, which is paralleled by higher pollen viability in silencing lines. ANRi transgenic lines of strawberry provide a versatile tool for the study of the biological functions of proanthocyanidins.
Fruit colour is central to the sensorial and nutritional quality of strawberry fruit and is therefore a major target in breeding programmes of the octoploid cultivated strawberry (
). The red colour ...of the fruit is caused by the accumulation of anthocyanins, which are water-soluble flavonoids. To facilitate molecular breeding, here we have mapped with high resolution fruit colour quantitative trait loci (QTLs) (COLOUR, scored visually as in selection programmes) and associated flavonoid metabolic QTLs (5 anthocyanins compounds together with 8 flavonols and flavan-3-ols) to specific subgenomes of cultivated strawberry. Two main colour-related QTLs were located on the LG3A linkage group (
subgenome). Genetic mapping, transcriptome analysis and whole genome sequencing enabled the detection of a homoeo-allelic variant of
(
underlying the major male M3A COLOUR and pelargonidin-3-glucoside (PgGs) QTLs (up to ∼20% of explained variance). Consistent with previously published functional studies,
transcript abundance was inversely related with PgGs content in contrasted progeny individuals. Genetic segregation analyses further indicated that a molecular marker designed using an 18 bp deletion found in the 5'UTR of the candidate
homoeo-allelic variant is effective in identifying genotypes with intense red fruit colour. Our study provides insights into the genetic and molecular control of colour-related traits in strawberry and further defines a genetic marker for marker-assisted selection of new strawberry varieties with improved colour. The QTLs detected and the underlying candidate genes are different from those described to date, emphasising the importance of screening a wide diversity of genetic resources in strawberry.
This work characterized the role of the R2R3-MYB10 transcription factor (TF) in strawberry fruit ripening. The expression of this TF takes place mainly in the fruit receptacle and is repressed by ...auxins and activated by abscisic acid (ABA), in parallel to the ripening process. Anthocyanin was not produced when FaMYB10 expression was transiently silenced in fruit receptacles. An increase in FaMYB10 expression was observed in water-stressed fruits, which was accompanied by an increase in both ABA and anthocyanin content. High-throughput transcriptomic analyses performed in fruits with downregulated FaMYB10 expression indicated that this TF regulates the expression of most of the Early-regulated Biosynthesis Genes (EBGs) and the Late-regulated Biosynthesis Genes (LBGs) genes involved in anthocyanin production in ripened fruit receptacles. Besides, the expression of FaMYB10 was not regulated by FaMYB1 and vice versa. Taken together, all these data clearly indicate that the Fragaria × ananassa MYB10 TF plays a general regulatory role in the flavonoid/phenylpropanoid pathway during the ripening of strawberry
Phenolics have health-promoting properties and are a major group of metabolites in fruit crops. Through reverse genetic analysis of the functions of four ripening-related genes in the octoploid ...strawberry (Fragaria×ananassa), we discovered four acylphloroglucinol (APG)-glucosides as nativeFragariaspp. fruit metabolites whose levels were differently regulated in the transgenic fruits. The biosynthesis of the APG aglycones was investigated by examination of the enzymatic properties of three recombinantFragaria vescachalcone synthase (FvCHS) proteins. CHS is involved in anthocyanin biosynthesis during ripening. TheF. vescaenzymes readily catalyzed the condensation of two intermediates in branched-chain amino acid metabolism, isovaleryl-Coenzyme A (CoA) and isobutyryl-CoA, with three molecules of malonyl-CoA to form phlorisovalerophenone and phlorisobutyrophenone, respectively, and formed naringenin chalcone when 4-coumaroyl-CoA was used as starter molecule. Isovaleryl-CoA was the preferred starter substrate ofFvCHS2-1. Suppression ofCHSactivity in both transient and stableCHSsilenced fruit resulted in a substantial decrease of APG glucosides and anthocyanins and enhanced levels of volatiles derived from branched-chain amino acids. The proposed APG pathway was confirmed by feeding isotopically labeled amino acids. Thus,Fragariaspp. plants have the capacity to synthesize pharmaceutically important APGs using dual functionalCHS/(phloriso)valerophenone synthases that are expressed during fruit ripening. Duplication and adaptive evolution of CHS is the most probable scenario and might be generally applicable to other plants. The results highlight that important promiscuous gene function may be missed when annotation relies solely on in silico analysis.
The synthesis of pharmaceutically active acylphloroglucinols during strawberry fruit ripening is catalyzed by dual-function chalcone synthases/valerophenone synthases.
Phenolics have health-promoting ...properties and are a major group of metabolites in fruit crops. Through reverse genetic analysis of the functions of four ripening-related genes in the octoploid strawberry (
Fragaria × ananassa
), we discovered four acylphloroglucinol (
APG
)-glucosides as native
Fragaria
spp. fruit metabolites whose levels were differently regulated in the transgenic fruits. The biosynthesis of the
APG
aglycones was investigated by examination of the enzymatic properties of three recombinant
Fragaria vesca
chalcone synthase (FvCHS) proteins. CHS is involved in anthocyanin biosynthesis during ripening. The
F. vesca
enzymes readily catalyzed the condensation of two intermediates in branched-chain amino acid metabolism, isovaleryl-Coenzyme A (CoA) and isobutyryl-CoA, with three molecules of malonyl-CoA to form phlorisovalerophenone and phlorisobutyrophenone, respectively, and formed naringenin chalcone when 4-coumaroyl-CoA was used as starter molecule. Isovaleryl-CoA was the preferred starter substrate of FvCHS2-1. Suppression of
CHS
activity in both transient and stable
CHS
-silenced fruit resulted in a substantial decrease of
APG
glucosides and anthocyanins and enhanced levels of volatiles derived from branched-chain amino acids. The proposed
APG
pathway was confirmed by feeding isotopically labeled amino acids. Thus,
Fragaria
spp. plants have the capacity to synthesize pharmaceutically important
APG
s using dual functional CHS/(phloriso)valerophenone synthases that are expressed during fruit ripening. Duplication and adaptive evolution of CHS is the most probable scenario and might be generally applicable to other plants. The results highlight that important promiscuous gene function may be missed when annotation relies solely on in silico analysis.
This work characterized the role of the R2R3-MYB10 transcription factor (TF) in strawberry fruit ripening. The expression of this TF takes place mainly in the fruit receptacle and is repressed by ...auxins and activated by abscisic acid (ABA), in parallel to the ripening process. Anthocyanin was not produced when FaMYB10 expression was transiently silenced in fruit receptacles. An increase in FaMYB10 expression was observed in water-stressed fruits, which was accompanied by an increase in both ABA and anthocyanin content. High-throughput transcriptomic analyses performed in fruits with downregulated FaMYB10 expression indicated that this TF regulates the expression of most of the Early-regulated Biosynthesis Genes (EBGs) and the Late-regulated Biosynthesis Genes (LBGs) genes involved in anthocyanin production in ripened fruit receptacles. Besides, the expression of FaMYB10 was not regulated by FaMYB1 and vice versa. Taken together, all these data clearly indicate that the Fragaria x ananassa MYB10 TF plays a general regulatory role in the flavonoid/phenylpropanoid pathway during the ripening of strawberry
Metabolite profiling and quantitative genetics analyses uncover a strawberry peroxidase gene as an important factor controlling the flux to soluble (flavonoids) and insoluble (lignin) polyphenols in ...fruits
.
Plant phenolics have drawn increasing attention due to their potential nutritional benefits. Although the basic reactions of the phenolics biosynthetic pathways in plants have been intensively analyzed, the regulation of their accumulation and flux through the pathway is not that well established. The aim of this study was to use a strawberry (
Fragaria
×
ananassa
) microarray to investigate gene expression patterns associated with the accumulation of phenylpropanoids, flavonoids, and anthocyanins in strawberry fruit. An examination of the transcriptome, coupled with metabolite profiling data from different commercial varieties, was undertaken to identify genes whose expression correlated with altered phenolics composition. Seventeen comparative microarray analyses revealed 15 genes that were differentially (more than 200-fold) expressed in phenolics-rich versus phenolics-poor varieties. The results were validated by heterologous expression of the peroxidase
FaPRX27
gene, which showed the highest altered expression level (more than 900-fold). The encoded protein was functionally characterized and is assumed to be involved in lignin formation during strawberry fruit ripening. Quantitative trait locus analysis indicated that the genomic region of
FaPRX27
is associated with the fruit color trait. Down-regulation of the
CHALCONE SYNTHASE
gene and concomitant induction of
FaPRX27
expression diverted the flux from anthocyanins to lignin. The results highlight the competition of the different phenolics pathways for their common precursors. The list of the 15 candidates provides new genes that are likely to impact polyphenol accumulation in strawberry fruit and could be used to develop molecular markers to select phenolics-rich germplasm.
Short-chain esters contribute to the blend of volatiles that define the strawberry aroma. The last step in their biosynthesis involves an alcohol acyltransferase that catalyses the esterification of ...an acyl moiety of acyl-CoA with an alcohol. This study identified a novel strawberry alcohol acyltransferase gene (FaAAT2) whose expression pattern during fruit receptacle growth and ripening is in accordance with the production of esters throughout strawberry fruit ripening. The full-lengthFaAAT2cDNA was cloned and expressed inEscherichia coliand its activity was analysed with acyl-CoA and alcohol substrates. The semi-purified FaAAT2 enzyme had activity with C1–C8 straight-chain alcohols and aromatic alcohols in the presence of acetyl-CoA. Cinnamyl alcohol was the most efficient acyl acceptor. WhenFaAAT2expression was transiently downregulated in the fruit receptacle by agroinfiltration, the volatile ester production was significantly reduced in strawberry fruit. The results suggest thatFaAAT2plays a significant role in the production of esters that contribute to the final strawberry fruit flavour.
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