Differential regulation of phenylalanine ammonia lyase activity and protein level by light in tomato seedlings

Effect of cultivar, maturation stage, and year on sugar and phenolic composition of elderberries

BACKGROUND

The chemical composition, phenylalanine ammonia-lyase (PAL), polyphenol oxidase (PPO) and peroxidase (POD) activity of the three main Portuguese elderberry cultivars were determined for the first time through five stages of maturation, in different harvesting years, to gain a deeper understanding of the effect of climatic conditions and enzymatic activity involved in the synthesis and degradation of phenolic compounds on the final quality of elderberries.

RESULTS

Simple sugar and anthocyanin content increased with maturation but total acidity and flavonoids content decreased, and cinnamic acids did not show a clear trend. Climatic conditions seem to have a decisive influence on the elderberry maturation, namely the total number of hot (>30 °C) days. The PAL, PPO, and POD activity can explain the differences observed in elderberry phenolic content.

CONCLUSION

These results highlighted the influence of climatic conditions in each harvesting season on elderberry development and quality. © 2022 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Validation of Appropriate Reference Genes for qRT–PCR Normalization in Oat (Avena sativa L.) under UV-B and High-Light Stresses

Oat is a food and forage crop species widely cultivated worldwide, and it is also an important forage grass in plateau regions of China, where there is a high level of ultraviolet radiation and sunlight. Screening suitable reference genes for oat under UV-B and high-light stresses is a prerequisite for ensuring the accuracy of real-time quantitative PCR (qRT–PCR) data used in plant adaptation research. In this study, eight candidate reference genes (sulfite oxidase, SUOX; victorin binding protein, VBP; actin-encoding, Actin1; protein PSK SIMULATOR 1-like, PSKS1; TATA-binding protein 2-like, TBP2; ubiquitin-conjugating enzyme E2, UBC2; elongation factor 1-alpha, EF1-α; glyceraldehyde-3-phosphate dehydrogenase 1, GAPDH1;) were selected based on previous studies and our oat transcriptome data. The expression stability of these reference genes in oat roots, stems, and leaves under UV-B and high-light stresses was first calculated using three frequently used statistical software (geNorm, NormFinder, and BestKeeper), and then the comprehensive stability of these genes was evaluated using RefFinder. The results showed that the most stably expressed reference genes in the roots, stems, and leaves of oat under UV-B stress were EF1-α, TBP2, and PSKS1, respectively; the most stably expressed reference genes in the roots, stems, and leaves under high-light stress were PSKS1, UBC2, and PSKS1, respectively. PSKS1 was the most stably expressed reference gene in all the samples. The reliability of the selected reference genes was further validated by analysis of the expression of the phenylalanine ammonia-lyase (PAL) gene. This study highlights reference genes for accurate quantitative analysis of gene expression in different tissues of oat under UV-B and high-light stresses.

Gene expression pattern and taxane biosynthesis in a cell suspension culture of Taxus baccata L. subjected to light and a phenylalanine ammonia lyase (PAL) inhibitor

Taxus baccata L. cell culture is a promising commercial method for the production of taxanes with anti-cancer activities. In the present study, a T. baccata cell suspension culture was exposed to white light and 2-aminoindan-2-phosphonic acid (AIP), a phenylalanine ammonia lyase (PAL) inhibitor, and the effects of this treatment on cell growth, PAL activity, total phenol content (TPC), total flavonoid content (TFC), taxane production and the expression of some key taxane biosynthetic genes (DXS, GGPPS, T13OH, BAPT, DBTNBT) as well as the PAL were studied. Light reduced cell growth, whereas AIP slightly improved it. Light increased PAL activity up to 2.7-fold relative to darkness. The highest TPC (24.89 mg GAE/g DW) and TFC (66.94 mg RUE/g DW) were observed in cultures treated with light and AIP. Light treatment also resulted in the maximum content of total taxanes (154.78 μg/g DW), increasing extracellular paclitaxel and cephalomannin (3.3-fold) and intracellular 10-deacetyl paclitaxel (2.5-fold). Light significantly increased the expression level of PAL, DBTNBT, BAPT, and T13αOH genes, whereas it had no effect on the expression of DXS, a gene active at the beginning of the taxane biosynthetic pathway. AIP had no significant effect on the expression of the target genes. In conclusion, the light-induced activation of PAL transcription and altered expression of relevant biosynthetic genes reduced cell growth and increased the content of total phenolic compounds and taxanes. These findings can be applied to improve taxane production in controlled cultures and bioreactors.

Interactive effects of nitrogen, UV and PAR on barley morphology and biochemistry are associated with the leaf C:N balance

Environmental conditions to which plants acclimate prior exposure to abiotic or biotic stressors can greatly affect their subsequent resilience. This may have a significant impact on the response to ongoing climate change and can be useful for increasing the food security under adverse weather conditions associated with climate change.Within this study, we tested the hypothesis that plant morphological and biochemical acclimation to radiation conditions and nitrogen (N) availability is closely linked with carbon (C) and N balance. Four barley (Hordeum vulgare) varieties, differing in their morphological characteristics and sensitivity to photooxidative stress, were grown at two levels of N supply and four radiation regimes combining distinct levels of ultraviolet (UV) and photosynthetically active radiation (PAR). Changes in root and shoot morphology, accumulation of phenolic compounds, amino acids, and sugars were studied together with the analysis of C and N content in leaves. Both UV and PAR reduced leaf length and increased root-to-shoot ratio (R:S). Such effect was more pronounced under high N availability. High N supply reduced R:S, but this effect showed significant interactions with UV and PAR, and also with barley variety. Changes in R:S were positively related to C:N ratio in leaves that varied in response to both N availability and radiation treatments. UV radiation, particularly in combination with high PAR intensity, led to increases in most phenolic compounds (particularly flavones such as saponarin, homoorientin and isovitexin) which was also closely associated with changes in C:N ratio, while specifically phenolic acids (vanillic and syringic acids) decreased under high levels of UV and PAR, and hydroxycinnamic acids responded positively mainly to PAR. Although high N availability generally reduced the accumulation of phenolic compounds, this effect was genotype-specific and modulated by the radiation regime. A similar antagonistic effect of radiation treatment and N availability was also found for the accumulation of sugars (pentoses), resulting in a close relationship between the accumulation of pentoses and C:N ratio. The accumulation of most amino acids, in contrary to phenolic compounds, increases at high N and is also stimulated by high PAR and UV intensities. We conclude that radiation conditions and N availability have opposite effects on plant morphology and accumulation of most phenolic compounds and modulate the amino acid and sugar metabolism. Strong associations of these responses with changes in C:N ratio indicates that plant stoichiometry integrates acclimation processes and induction of relevant defence mechanisms.

Effects of Laccaria bicolor on Gene Expression of Populus trichocarpa Root under Poplar Canker Stress

Poplars can be harmed by poplar canker. Inoculation with mycorrhizal fungi can improve the resistance of poplars to canker, but the molecular mechanism is still unclear. In this study, an aseptic inoculation system of L. bicolor-P. trichocarpa-B. dothidea was constructed, and transcriptome analysis was performed to investigate regulation by L. bicolor of the expression of genes in the roots of P. trichocarpa during the onset of B. dothidea infection, and a total of 3022 differentially expressed genes (DEGs) were identified. Weighted correlation network analysis (WGCNA) was performed on these DEGs, and 661 genes' expressions were considered to be affected by inoculation with L. bicolor and B. dothidea. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses showed that these 661 DEGs were involved in multiple pathways such as signal transduction, reactive oxygen metabolism, and plant-pathogen interaction. Inoculation with L. bicolor changed the gene expression pattern of the roots, evidencing its involvement in the disease resistance response of P. trichocarpa. This research reveals the mechanism of L. bicolor in inducing resistance to canker of P. trichocarpa at the molecular level and provides a theoretical basis for the practical application of mycorrhizal fungi to improve plant disease resistance.

Study on the molecular mechanism of Laccaria bicolor helping Populus trichocarpa to resist the infection of Botryosphaeria dothidea

AIMS

This study explored the specific molecular mechanism of Laccaria bicolor to help Populus trichocarpa resist infection by Botryosphaeria dothidea.

METHODS AND RESULTS

Transcriptome technology was used to sequence P. trichocarpa under disease stress, and a total of 6379 differentially expressed genes (DEGs) were identified. A total of 536 new DEGs were induced by L. bicolor during the infection of B. dothidea. L. bicolor helps to prevent and alleviate the infection of B. dothidea by regulating related genes in the cell wall pathway, signal transduction pathway, disease-resistant protein synthesis pathway and antioxidant enzyme synthesis pathway of P. trichocarpa.

CONCLUSION

The inoculation of L. bicolor can regulate the expression of genes in the cell wall pathway and enhance the physical defense capabilities of plants. Under disease stress conditions, L. bicolor can regulate signal transduction pathways, disease-resistant related pathways and reactive oxygen species (ROS) clearance pathways to help P. trichocarpa alleviate the disease.

SIGNIFICANCE AND IMPACT OF THE STUDY

The research reveals the mechanism of L. bicolor inducing resistance to canker of P. trichocarpa from the molecular level and provides a theoretical basis for the practical application of mycorrhizal fungi to improve plant disease resistance.

Comparative Analysis of Proteomics and Transcriptomics during Fertility Transition in a Two-Line Hybrid Rice Line Wuxiang S

The two-line hybrid rice is an important factor of a global crop, but its fertility transition mechanism is unclear. Here, a comparative proteomics and transcriptomics analysis was completed on the two-line hybrid rice line Wuxiang S (WXS) to explore its molecular mechanism and protein regulation during fertility transition. A total of 340 differentially abundant proteins (DAPs) were identified using iTRAQ between the pollen mother cell formation stage (P2) and the meiosis stage (P3). There were 3541 and 4247 differentially expressed genes (DEGs) in P2 and P3 between WXS (Sterile, S)-WXS(S) and WXS (Fertile, F)-WXS(F), respectively, of which 92 and 71 DEGs had corresponding DAPs. Among the DAPs and DEGs, 65 (SP2 vs. FP2) and 55 (SP3 vs. FP3) corresponding DEGs and DAPs (cor-DEGs-DAPs) showed the same expression trend, indicating the cor-DEGs-DAPs genes might play vital roles in WXS fertility transition. Further analysis indicated that cor-DEGs-DAPs proteins were related to energy metabolism-related proteins in anther development and were accompanied by the activation of the stress response pathway and modifications to the cell wall, which ultimately affected the fertility transition of the PTGMS rice line WXS.

Hydrogen sulfide directs metabolic flux towards the lignan biosynthesis in Linum album hairy roots

Hydrogen sulfide (H₂S) has been recently found as an important signaling molecule especially in root system architecture of plants. The regulation of root formation through H₂S has been reported in previous works; while the profiling of metabolites in response to H₂S is not clearly discussed. To this end, different concentrations of sodium hydrosulfide (an H₂S donor) were applied to the culture of Linum album hairy roots. Subsequently, the amino acid profiles, soluble carbohydrates, and central intermediates of phenylpropanoid pathway with two branches of lignans and flavonoids were assessed by spectroscopy and high performance liquid chromatography techniques. An analysis of the signaling molecules (nitric oxide, hydrogen peroxide, and salicylic acid) was also conducted as they proposed to act in conjunction with H₂S. The H₂S activated antioxidant systems and caused a shift from flavonoid to lignan production (podophyllotoxin and 6-methoxypodophyllotoxin); although, some of the flavonoids increased in a dose-dependent manner. The H₂S decreased the contents of phenylalanine and tyrosine as substrates of the phenylpropanoid pathway, but increased proline and histidine as an osmolyte and antioxidant, respectively. These findings propose that H₂S modulates other signaling molecules, regulates free amino acids, and mediates biosynthesis of lignans and flavonoids in the phenylpropanoids biosynthesis pathway.

Induction of phenolic compounds by UV and PAR is modulated by leaf ontogeny and barley genotype

We investigated the effect of leaf ontogeny and barley genotype on the accumulation of phenolic compounds (PhCs) induced by ultraviolet (UV) and photosynthetically active radiation (PAR). We hypothesized that different groups of PhCs are induced in leaves differing in ontogeny, and that this has consequences for protective functions and the need for other protection mechanisms. Generally, lower constitutive contents of PhCs (under conditions of UV exclusion and reduced PAR) were found in a UV-sensitive genotype (Barke) compared to a tolerant genotype (Bonus). However, UV and PAR induced accumulation of PhCs exceeded the constitutive amounts several fold. Specifically, lutonarin, 3-feruloylquinic acid, unidentified hydroxycinnamic acid and luteolin derivatives were markedly enhanced by high PAR and UV irradiances. Leaves developed during UV and PAR treatments had higher PhCs contents than mature leaves already fully developed at the onset of the UV and PAR treatment. UV and PAR treatments had, however, a minor effect on saponarin and unidentified apigenin derivatives which occur particularly in mature leaves of the tolerant genotype Bonus. In addition, high UV and PAR intensities increased the total content of xanthophylls (VAZ), while chlorophyll content was reduced, particularly in developing leaves. A redundancy analysis revealed positive associations between most of PhCs and VAZ and a negative association between total chlorophylls and carotenoids. Non-linear relationships between VAZ and lutonarin and other PhCs indicate that VAZ accumulation can compensate for the insufficient efficiency of anti-oxidative protection mediated by PhCs. Accordingly, we conclude that UV and PAR-induced accumulation of PhCs is affected by leaf ontogeny, however, this effect is compound-specific.

Piriformospora indica cell wall modulates gene expression and metabolite profile in Linum album hairy roots

Elicitation of Linum album hairy roots by Piriformospora indica cell wall induced the target genes and specific metabolites in phenylpropanoid pathway and shifted the amino acid metabolism toward the phenolic compound production. Plants have evolved complex mechanisms to defend themselves against various biotic stresses. One of these responses is the production of metabolites that act as defense compounds. Manipulation of plant cell cultures by biotic elicitors is a useful strategy for improving the production of valuable secondary metabolites. This study focused on hairy root culture of Linum album, an important source for lignans. The effects of cell wall elicitor extracted from Piriformospora indica on phenylpropanoid derivatives were evaluated to identify metabolic traits related to biotic stress tolerance. Significant increases in lignin, lignans; lariciresinol, podophyllotoxin, and 6-methoxy podophyllotoxin; phenolic acids: cinnamic acid, ferulic acid, and salicylic acid; flavonoids: myricetin, kaempferol, and diosmin were observed in response to the fungal elicitor. In addition, the gene expression levels of phenylalanine ammonia-lyase, cinnamyl alcohol dehydrogenase, cinnamoyl-CoA reductase, and pinoresinol-lariciresinol reductase significantly increased after elicitation. The composition of free amino acids was altered under the elicitation. Phenylalanine and tyrosine, as precursors of phenylpropanoid metabolites, were increased, but alanine, serine, and glutamic acid significantly decreased in response to the fungal elicitor, suggesting that the amino acid pathway may be shifted toward biosynthesis of aromatic amino acids and precursors of the phenylpropanoid pathway. These results provided evidence that up-regulation of genes involved in the phenylpropanoid pathway in response to the fungal elicitor resulted in enhanced metabolic responses associated with the protection in L. album. This approach can also be applied to improve lignan production.

In vitro polyploidy induction: changes in morphology, podophyllotoxin biosynthesis, and expression of the related genes in Linum album (Linaceae)

Induction of tetraploidy was performed and podophyllotoxin production increased by upregulating the expression level and enzyme activity of genes related to its biosynthesis in tetraploid compared to diploid Linum album. Linum album is a valuable medicinal plant that produces antiviral and anticancer compounds including podophyllotoxin (PTOX). To achieve homogeneous materials, in vitro diploid clones were established, and their nodal segments were exposed to different concentrations and durations of colchicine. This resulted in successful tetraploidy induction, confirmed by flow cytometry, and is being reported for the first time. The highest efficiency of tetraploid induction (22%) was achieved after 72 h exposure to 2.5-mM colchicine treatment. The stable tetraploids were produced after being subcultured three times, and their ploidy stability was confirmed after each subculture. The effects of autopolyploidy were measured on the morphological and phytochemical characteristics, as well as enzyme activity and the expression levels of some key genes involved in the PTOX biosynthetic pathway, including phenylalanine ammonia-lyase (PAL), cinnamoyl-Coa reductase (CCR), cinnamyl-alcohol dehydrogenase (CAD), and pinoresinol-lariciresinol reductase (PLR). The tetraploid plants had larger leaves and stomata (length and width) and lower density stomata. Increasing the ploidy level from diploid to tetraploid resulted in 1.39- and 1.23-fold enhancement of PTOX production, respectively, in the leaves and stem. The increase in PTOX content was associated with upregulated activities of some enzymes studied related to its biosynthetic pathway and the expression of the corresponding genes. The expression of the PAL gene and PLR enzymatic activity had the most positive correlation with the ploidy level in both leaf and stem tissues. Our results verified that autotetraploid induction is a useful breeding method, remarkably increasing the PTOX content in the leaves and stem of L. album.

Metabolite profiling and transcript analysis reveal specificities in the response of a berry derived cell culture to abiotic stresses

As climate changes, there is a need to understand the expected effects on viticulture. In nature, stresses exist in a combined manner, hampering the elucidation of the effect of individual cues on grape berry metabolism. Cell suspension culture originated from pea-size Gamy Red grape berry was used to harness metabolic response to high light (HL; 2500 μmol m(-2)s(-1)), high temperature (HT; 40°C) and their combination in comparison to 25°C and 100 μmol m(-2)s(-1) under controlled condition. When LC-MS and GC-MS based metabolite profiling was implemented and integrated with targeted RT-qPCR transcript analysis specific responses were observed to the different cues. HL enhanced polyphenol metabolism while HT and its combination with HL induced amino acid and organic acid metabolism with additional effect on polyphenols. The trend of increment in TCA cycle genes like ATCs, ACo1, and IDH in the combined treatment might support the observed increment in organic acids, GABA shunt, and their derivatives. The apparent phenylalanine reduction with polyphenol increment under HL suggests enhanced fueling of the precursor toward the downstream phenylpropanoid pathway. In the polyphenol metabolism, a differential pattern of expression of flavonoid 3',5' hydroxylase and flavonoid 3' hydroxylase was observed under high light (HL) and combined cues which were accompanied by characteristic metabolite profiles. HT decreased glycosylated cyanidin and peonidin forms while the combined cues increased acetylated and coumarylated peonidin forms. Transcription factors regulating anthocyanin metabolism and their methylation, MYB, OMT, UFGT, and DFR, were expressed differentially among the treatments, overall in agreement with the metabolite profiles. Taken together these data provide insights into the coordination of central and secondary metabolism in relation to multiple abiotic stresses.

Concurrent overactivation of the cytosolic glutamine synthetase and the GABA shunt in the ABA-deficient sitiens mutant of tomato leads to resistance against Botrytis cinerea

Deficiency of abscisic acid (ABA) in the sitiens mutant of tomato (Solanum lycopersicum) culminates in increased resistance to Botrytis cinerea through a rapid epidermal hypersensitive response (HR) and associated phenylpropanoid pathway-derived cell wall fortifications. This study focused on understanding the role of primary carbon : nitrogen (C : N) metabolism in the resistance response of sitiens to B. cinerea. How alterations in C : N metabolism are linked with the HR-mediated epidermal arrest of the pathogen has been also investigated. Temporal alterations in the γ-aminobutyric acid (GABA) shunt, glutamine synthetase/glutamate synthase (GS/GOGAT) cycle and phenylpropanoid pathway were transcriptionally, enzymatically and metabolically monitored in both wild-type and sitiens plants. Virus-induced gene silencing, microscopic analyses and pharmacological assays were used to further confirm the data. Our results on the sitiens-B. cinerea interaction favor a model in which cell viability in the cells surrounding the invaded tissue is maintained by a constant replenishment of the tricarboxylic acid (TCA) cycle through overactivation of the GS/GOGAT cycle and the GABA shunt, resulting in resistance through both tightly controlling the defense-associated HR and slowing down the pathogen-induced senescence. Collectively, this study shows that maintaining cell viability via alterations in host C : N metabolism plays a vital role in the resistance response against necrotrophic pathogens.

The effect of light on gene expression and podophyllotoxin biosynthesis in Linum album cell culture

Podophyllotoxin (PTOX) is a naturally occurring phenolic compound isolated as an active anti-tumor agent. The stimulatory influence of light on the formation of phenolic compounds has been reported, but the molecular mechanism underlying the effect of light on the expression of genes involved in phenolic biosynthesis, especially of lignans, is still not fully understood. A series of experiments was carried out using ordinary fluorescent lamps to study the influence of light irradiation on growth and PTOX accumulation in Linum album cell cultures by varying the type of light and periods of exposure. The biosynthesis of PTOX was variably affected according to the quality of light. The enhancing effects of red light on PTOX production was correlated with increased activities of the enzyme phenylalanine ammonia-lyase (PAL), and the expression of some key genes involved in the biosynthesis of this compound, including the PAL gene itself and the cinnamoyl-CoA reductase (CCR) gene. Blue light was found to have similar effects but mainly on the expression level of CCR and pinoresinol lariciresinol reductase (PLR) genes.

The impact of long-term CO2 enrichment on sun and shade needles of Norway spruce (Picea abies): photosynthetic performance, needle anatomy and phenolics accumulation

Norway spruce (Picea abies L. Karst) grown under ambient (365-377 μmol(CO(2)) mol(-1); AC) and elevated (700 μmol(CO(2)) mol(-1); EC) CO(2) concentrations within glass domes with automatically adjustable windows and on an open-air control site were studied after 8 years of treatment. The effect of EC on photosynthesis, mesophyll structure and phenolics accumulation in sun and shade needles was examined. Photosynthetic assimilation and dark respiration rates were measured gasometrically; the structural parameters of mesophyll were determined using confocal microscopy and stereological methods. The contents of total soluble phenolics and lignin were assessed spectrophotometrically, and localizations of different phenolic groups were detected histochemically on needle cross-sections. EC enhanced the light-saturated CO(2) assimilation rate and reduced dark respiration in the current-year needles. No effects of CO(2) enrichment on mesophyll structural parameters were observed. Similarly, the accumulation and localization of phenolics and lignin remained unaffected by EC treatment. Needles differentiated into sun and shade ecotypes in the same manner and to the same extent irrespective of CO(2) treatment. Based on these results, it is apparent that the EC-induced enhancement of photosynthesis is not related to changes in the examined structural parameters of mesophyll and accumulation of phenolic compounds.

Inhibition of the ubiquitin-proteasome pathway alters cellular levels of nitric oxide in tomato seedlings

Nitric oxide (NO) is involved in diverse plant growth processes; however, little is known about pathways regulating NO levels in plants. In this study, we isolated a NO-overproducing mutant of tomato (Solanum lycopersicum) in which hyper-accumulation of NO, associated with increase in nitric oxide synthase (NOS)-like activity, caused diminished vegetative growth of plants and showed delayed flowering. The hyper-accumulation of NO caused drastic shortening of primary root (shr) in the seedlings, while the scavenging of NO restored root elongation in shr mutant. Inhibition of NOS-like activity reduced NO levels and stimulated root elongation in the shr mutant seedlings, while inhibition of nitrate reductase (NR) activity could not rescue shr phenotype. The stimulation of NO levels in shr mutant also conferred increased resistance to pathogen Pseudomonas syringae. Application of pharmacological inhibitors regulating ubiquitin-proteasome pathway reduced NO levels and NOS-like activity and stimulated shr root elongation. Our data indicate that a signaling pathway involving regulated protein degradation likely regulates NO synthesis in tomato.

Phenylpropanoid Metabolism in Ripening Fruits

  Ripening of fleshy fruit is a differentiation process involving biochemical and biophysical changes that lead to the accumulation of sugars and subsequent changes in tissue texture. Also affected are phenolic compounds, which confer color, flavor/aroma, and resistance to pathogen invasion and adverse environmental conditions. These phenolic compounds, which are the products of branches of the phenylpropanoid pathway, appear to be closely linked to fruit ripening processes. Three key enzymes of the phenylpropanoid pathway, namely phenylalanine ammonia lyase, O-methyltransferase, and cinnamyl alcohol dehydrogenase (CAD) have been reported to modulate various end products including lignin and protect plants against adverse conditions. In addition, peroxidase, the enzyme following CAD in the phenylpropanoid pathway, has also been associated with injury, wound repair, and disease resistance. However, the role of these enzymes in fruit ripening is a matter of only recent investigation and information is lacking on the relationships between phenylpropanoid metabolism and fruit ripening processes. Understanding the role of these enzymes in fruit ripening and their manipulation may possibly be valuable for delineating the regulatory network that controls the expression of ripening genes in fruit. This review elucidates the functional characterization of these key phenylpropanoid biosynthetic enzymes/genes during fruit ripening processes.

Post-veraison sunlight exposure induces MYB-mediated transcriptional regulation of anthocyanin and flavonol synthesis in berry skins of Vitis vinifera

Anthocyanins, flavan-3-ols, and flavonols are the three major classes of flavonoid compounds found in grape berry tissues. Several viticultural practices increase flavonoid content in the fruit, but the underlying genetic mechanisms responsible for these changes have not been completely deciphered. The impact of post-veraison sunlight exposure on anthocyanin and flavonol accumulation in grape berry skin and its relation to the expression of different transcriptional regulators known to be involved in flavonoid synthesis was studied. Treatments consisting of removing or moving aside the basal leaves which shade berry clusters were applied. Shading did not affect sugar accumulation or gene expression of HEXOSE TRANSPORTER 1, although in the leaf removal treatment, these events were retarded during the first weeks of ripening. Flavonols were the most drastically reduced flavonoids following shading and leaf removal treatments, related to the reduced expression of FLAVONOL SYNTHASE 4 and its putative transcriptional regulator MYB12. Anthocyanin accumulation and the expression of CHS2, LDOX, OMT, UFGT, MYBA1, and MYB5a genes were also affected. Other regulatory genes were less affected or not affected at all by these treatments. Non-transcriptional control mechanisms for flavonoid synthesis are also suggested, especially during the initial stages of ripening. Although berries from the leaf removal treatment received more light than shaded fruits, malvidin-3-glucoside and total flavonol content was reduced compared with the treatment without leaf removal. This work reveals that flavonol-related gene expression responds rapidly to field changes in light levels, as shown by the treatment in which shaded fruits were exposed to light in the late stages of ripening. Taken together, this study establishes MYB-specific responsiveness for the effect of sun exposure and sugar transport on flavonoid synthesis.