Proanthocyanidins (PAs) and anthocyanins are two vital groups of flavonoid compounds for grape berries and red wines. Several transcription factors (TFs) have been identified to be involved in ...regulating PA and anthocyanin biosynthesis in grape berries. However, research on TFs with different regulatory mechanisms for these two biosynthesis branches in grapes remains limited. In this study, we identified an R2R3-MYB TF, VviMYB86, whose spatiotemporal gene expression pattern in grape berries coincided well with PA accumulation but contrasted with anthocyanin synthesis. Both
and
experiments verified that VviMYB86 positively regulated PA biosynthesis, primarily by upregulating the expression of the two leucoanthocyanidin reductase (LAR) genes in the Arabidopsis protoplast system, as well as in
-overexpressing grape callus cultured under 24 h of darkness. Moreover, VviMYB86 was observed to repress the anthocyanin biosynthesis branch in grapes by downregulating the transcript levels of
and
. Overall, VviMYB86 is indicated to have a broad effect on flavonoid synthesis in grape berries. The results of this study will help elucidate the regulatory mechanism governing the expression of the two LAR genes in grape berries and provide new insights into the regulation of PA and anthocyanin biosynthesis in grape berries.
Proanthocyanidins (PAs) are natural polymers of flavan-3-ols, commonly (+)-catechin and (-)-epicatechin. However, exactly how PA oligomerization proceeds is poorly understood. Here we show, both ...biochemically and genetically, that ascorbate (AsA) is an alternative "starter unit" to flavan-3-ol monomers for leucocyanidin-derived (+)-catechin subunit extension in the Arabidopsis thaliana anthocyanidin synthase (ans) mutant. These (catechin)
:ascorbate conjugates (AsA-C
) also accumulate throughout the phase of active PA biosynthesis in wild-type grape flowers, berry skins and seeds. In the presence of (-)-epicatechin, AsA-C
can further provide monomeric or oligomeric PA extension units for non-enzymatic polymerization in vitro, and their role in vivo is inferred from analysis of relative metabolite levels in both Arabidopsis and grape. Our findings advance the knowledge of (+)-catechin-type PA extension and indicate that PA oligomerization does not necessarily proceed by sequential addition of a single extension unit. AsA-C
defines a new type of PA intermediate which we term "sub-PAs".
Proanthocyanidins (PAs) and anthocyanins are flavonoids that contribute to the quality and health benefits of grapes and wine. Salinity affects their biosynthesis, but the underlying mechanism is ...still unclear. We studied the effects of NaCl stress on PA and anthocyanin biosynthesis in grape suspension cells derived from berry skins of
L. Cabernet Sauvignon using metabolite profiling and transcriptome analysis. We treated the cells with low (75 mM NaCl) and high (150 mM NaCl) salinity for 4 and 7 days. High salinity inhibited cell growth and enhanced PA and anthocyanin accumulation more than low salinity. The salinity-induced PAs and anthocyanins lacked C5'-hydroxylation modification, suggesting the biological significance of delphinidin- and epigallocatechin-derivatives in coping with stress. The genes up-regulated by salinity stress indicated that the anthocyanin pathway was more sensitive to salt concentration than the PA pathway, and WGCNA analysis revealed the coordination between flavonoid biosynthesis and cell wall metabolism under salinity stress. We identified transcription factors potentially involved in regulating NaCl dose- and time-dependent PA and anthocyanin accumulation, showing the dynamic remodeling of flavonoid regulation network under different salinity levels and durations. Our study provides new insights into regulator candidates for tailoring flavonoid composition and molecular indicators of salt stress in grape cells.
Proanthocyanidins (PAs) derived from grape berries determine the astringency and bitterness of red wines. The two leucoanthocyanidin reductases (VviLAR1 and VviLAR2) are crucial for PA accumulation ...in grapevine. Our previous studies show that the promoter of
contains multiple proposed bHLH transcription factor binding sites, but the corresponding bHLH family regulators remain unknown. Here we identified and functionally characterized VvibHLH93 as a new bHLH transcription factor in PA pathway. Yeast one-hybrid and electrophoretic mobility shift assays showed that VvibHLH93 bound the E/G-box in
promoter. And
gene was mainly expressed in grape flowers, tendrils, stems and berries at PA active stages. Overexpression of
suppressed PA accumulation in grape callus, which was linked to the repression of the transcript levels of two
s. The gene expression analysis in transgenic grape callus and the dual-luciferase assay in tobacco leaves together revealed that VvibHLH93 targeted a broad set of structural genes and transcription factors in flavonoid pathway. This research enriches the regulatory mechanism of the two
genes, and provides new insights into regulating PA content in grape berries.
The conversion of lignocellulosic feedstocks to fermentable sugar for biofuel production is inefficient, and most strategies to enhance efficiency directly target lignin biosynthesis, with associated ...negative growth impacts. Here we demonstrate, for both laboratory- and field-grown plants, that expression of Pag-miR408 in poplar (Populus alba × P. glandulosa) significantly enhances saccharification, with no requirement for acid-pretreatment, while promoting plant growth. The overexpression plants show increased accessibility of cell walls to cellulase and scaffoldin cellulose-binding modules. Conversely, Pag-miR408 loss-of-function poplar shows decreased cell wall accessibility. Overexpression of Pag-miR408 targets three Pag-LACCASES, delays lignification, and modestly reduces lignin content, S/G ratio and degree of lignin polymerization. Meanwhile, the LACCASE loss of function mutants exhibit significantly increased growth and cell wall accessibility in xylem. Our study shows how Pag-miR408 regulates lignification and secondary growth, and suggest an effective approach towards enhancing biomass yield and saccharification efficiency in a major bioenergy crop.
Glycosylated volatile precursors are important, particularly in wine grape berries, as they contribute to the final aroma in wines by releasing volatile aglycones during yeast fermentation and wine ...storage. Previous study demonstrated that VviGT14 was functioned as a critical monoterpene glucosyltransferase in grape berry, while the transcriptional regulation mechanism of
was still unknown. Here we identified VviWRKY40 as a binding factor of
promoter by both DNA pull-down and yeast one-hybrid screening, followed by a series of in vitro verification.
expression pattern negatively correlated with that of
in grape berries. And the suppressor role of VviWRKY40 was further confirmed by using the dual luciferase assay with Arabidopsis protoplast and grape cell suspension system. Furthermore, the grape suspension cell ABA treatment study showed that ABA downregulated
transcript level but promoted that of
, indicating that VviWRKY40 was at the downstream of ABA signal transduction network to regulate monoterpenoid glycosylation. These data extend our knowledge of transcriptional regulation of
, and provide new targets for grape breeding to alter monoterpenoid composition.
Norisoprenoids are important aromatic volatiles contributing to the pleasant floral/fruity odor in grapes and wine. They are produced from carotenoids through the cleavage of carotenoid cleavage ...dioxygenases (CCDs). However, the underlying mechanisms regulating
expression remain poorly understood. In this study, we showed that
expression was positively correlated with the accumulation of β-damascenone, β-ionone, 6-methyl-5-hepten-2-one, geranylacetone, dihydroedulan I, and total norisoprenoids in developing grapes in two vintages from two regions.
was found to be principally expressed in flowers, mature leaves, and berries. Abscisic acid strongly induced the expression of this gene. Additionally, the present study preliminarily indicated that the activity of the
promoter was dropped under 37°C treatment and also responded to the illumination change.
was expressed in parallel with
in developing grape berries. The latter is a MADS family transcription factor and nucleus-localized protein that was captured by yeast one-hybrid. A dual-luciferase reporter assay in tobacco leaves revealed that VvMADS4 downregulated the activity of the
promoter.
overexpression in grape calli and
Rehd. leaves repressed the
expression. In summary, this work demonstrates that
expression is positively correlated with the accumulation of norisoprenoids, and VvMADS4 is a potential negative regulator of
. Our results provide a new perspective for understanding the regulation of
expression and norisoprenoid accumulation in grapes.
To investigate the effect of light intensity on flavonoid biosynthesis, grapevine calluses were subjected to high light (HL, 250 μmol m−2 s−1) and dark (0 μmol m−2 s−1) in comparison to 125 μmol m−2 ...s−1 under controlled conditions (NL). The alteration of flavonoid profiles was determined and was integrated with RNA sequencing (RNA-seq)-based transcriptional changes of the flavonoid pathway genes. Results revealed that dark conditions inhibited flavonoid biosynthesis. Increasing light intensity affected flavonoids differently—the concentrations of flavonols and anthocyanins as well as the expressions of corresponding genes were less affected, whereas flavan-3-ol concentrations were predominantly increased, which caused enhanced trans-flavan-3-ol concentrations. Moreover, genes encoding leucoanthocyanidin reductase (LAR) exhibited different response patterns to light intensity changes—VviLAR1 expression increased with an increased light intensity, whereas VviLAR2 expression was insensitive. We further confirmed that the known transcription factors (TFs) involved in regulating flavan-3-ol biosynthesis utilized VviLAR1 as a target gene in grapevine calluses. In addition, VviLAR1 promoter activity was more sensitive to light intensity changes than that of VviLAR2 as determined using a transgenic Arabidopsis leaf system. These results suggested that light intensity had the most prominent effect on trans-flavan-3-ols in grapevine calluses and demonstrated that the two LAR genes had different response patterns to light intensity changes.
Proanthocyanidins (PAs) in grapevine (
) are found mainly in berries, and their content and degree of polymerization are important for the mouth feel of red wine. However, the mechanism of PA ...polymerization in grapevine remains unclear. Previous studies in the model legume
showed that 4β-(
-cysteinyl)-epicatechin (Cys-EC) is an epicatechin-type extension unit for nonenzymatic PA polymerization, and that leucoanthocyanidin reductase (LAR) converts Cys-EC into epicatechin starter unit to control PA extension. Grapevine possesses two
genes, but their functions are not clear. Here, we show that both Cys-EC and 4β-(
-cysteinyl)-catechin (Cys-C) are present in grapevine. Recombinant VvLAR1 and VvLAR2 convert Cys-C and Cys-EC into (+)-catechin and (-)-epicatechin, respectively, in vitro. The kinetic parameters of VvLARs are similar, with both enzymes being more efficient with Cys-C than with Cys-EC, the 2,3-cis conformation of which results in steric hindrance in the active site. Both VvLARs also produce (+)-catechin from leucocyanidin, and an inactive VvLAR2 allele reported previously is the result of a single amino acid mutation in the N terminus critical for all NADPH-dependent activities of the enzyme.
or
complement the
:
double mutant that also lacks the leucoanthocyanidin dioxygenase (LDOX) required for epicatechin starter unit formation, resulting in increased soluble PA levels, decreased insoluble PA levels, and reduced levels of Cys-C and Cys-EC when compared to the double mutant, and the appearance of catechin, epicatechin, and PA dimers characteristic of the
single mutant in young pods. These data advance our knowledge of PA building blocks and LAR function and provide targets for grapevine breeding to alter PA composition.
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•Four frequencies have been observed in the iso and aniso Raman spectra of EC.•Fermi constant W, NCE value V1 and V2 have been determined at different concentration.•Dimer structure ...and DFT calculations can reproduce the NCE and concentration effects.
The vibration band of the ring stretching (ν14), the fundamental ring breathing (ν17) and the Fermi resonance band of carbonyl stretching mixing with the overtone of the ring breathing (ν5 + 2ν17) have been investigated in solid ethylene carbonate (EC) and EC/CH3CN and EC/CHCl3 binary mixture. Dimer structure with aggregation-induced spectral splitting model (AIS) was applied to calculate the vibration spectra using the B3LYP-D3/6-311+G (d,p) procedure. The noncoincidence effect (NCE) and concentration induced frequency shifts of the ν14 and ν5 could be well explained by AIS model based on the dimer structure. Four bands were observed with two in the isotropic and two in the anisotropic Raman spectra and their NCE value decreased with the decrease of EC volume fraction in the binary mixture, and finally disappeared. NCE value and the Fermi resonance constants of EC at different concentrations were calculated from the experimental data.
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