Genotype-dependent regulation of vitamin E biosynthesis in olive fruits as revealed through metabolic and transcriptional profiles

Molecular and Biochemical Characterization of Olive 4-Hydroxyphenyl Pyruvate Dioxygenase Involved in the Biosynthesis of Tocopherols Present in Virgin Olive Oil

Olive (Olea europaea) fruit contains high amounts of tocopherols that are responsible, along with secoiridoid phenolic compounds, for most of the antioxidant and anti-inflammatory properties of virgin olive oil. This study focuses on the molecular and biochemical characterization of olive 4-hydroxyphenyl pyruvate dioxygenase (OeHPPD) catalyzing the biosynthesis of homogentisic acid, which constitutes the phenolic residue in the tocopherol molecule. OeHPPD is a cytoplasmic enzyme with a molecular weight of 49.8 kDa and a predicted tertiary structure very similar to the Arabidopsis enzyme that suggests similar catalytic mechanisms. OeHPPD has an estimated Kcat of 75.26 s-1 and catalytic efficiency (Km/Kcat) of 0.145 μM-1 s-1 with 4-hydroxyphenyl pyruvate as the substrate. The expression analysis in fruits from selected olive cultivars harvested at different ripening stages indicates that the OeHPPD gene is temporally regulated and cultivar-dependent. Moreover, the analysis of OeHPPD expression in fruits affected by drought stress suggests that HPPD is involved in olive environmental adaptation.

Accumulation Patterns of Metabolites Responsible for the Functional Quality of Virgin Olive Oil during Olive Fruit Ontogeny

The health-promoting antioxidant properties of virgin olive oil (VOO) are today considered priority targets in the new olive breeding programs. Given that these properties depend mainly on its phenolic fraction, whose origin lies in the phenolic compounds present in olive fruit, the objective of this study was to provide further insight into the accumulation dynamics of the main antioxidant compounds, including both polar phenolics and lipophilic tocopherols, during the ontogeny of the olive fruit. Data obtained show that, albeit with significant differences, all the studied genotypes share just after fruit set an intense increase in the synthesis of tyrosol and hydroxytyrosol derivatives, by far the main phenolic compounds of the olive fruit, and a subsequent steady decrease along fruit development and ripening. The accumulation dynamics of flavonoids and tocopherols were different from those of tyrosol and hydroxytyrosol derivatives, presenting a peak of synthesis just before the onset of fruit ripening, and then in general, their content decreases throughout the ripening phase. In the case of flavonoids, all genotypes also share a strong increase in the accumulation of anthocyanins in the final stages of fruit ripening, coinciding with the change in fruit color. Furthermore, the results during the fruit ripening process evidenced that the content of tyrosol and hydroxytyrosol derivatives and tocopherols in the fruit largely determines the content of these groups of compounds in the oil. The information acquired could be useful for the selection of the most suitable moment in the ontogeny of the olive fruit for the search for key genes in the biosynthesis of phenolic compounds.

Tocopherol Accumulation and Temporal Expression Analysis of VTE1 and VTE5 Gene Family in Fruit of Two Contrasting Avocado Genotypes

α-tocopherol is found in high concentrations in avocado fruit mesocarp, however, its accumulation and genetic control during maturation and ripening has not been elucidated. Based in the relevance of VTE1 and VTE5 genes in tocopherol biosynthesis and aiming to determine the association between tocopherol accumulation and expression of tocopherol biosynthetic genes, gene expression of VTE1 and VTE5 were evaluated through the time during three developmental stages: before harvest at 100, 160 and 220 days after flowering (DAF) and after harvest (220 DAF + 5) in two contrasting avocado genotypes (San Miguel and AVO40). San Miguel reached the highest levels at 220 DAF, whereas AVO40 increased α-tocopherol only after ripening (220 DAF + 5). A genome-wide search for VTE1 and VTE5 allowed to identify one and three genes, respectively. Both genotypes showed contrasting patterns of gene expression. Interestingly, AVO40 showed a highly positive correlation between α-tocopherol levels and gene expression of VTE1 and all VTE5 variants. On the other hand, San Miguel showed only a positive correlation between α-tocopherol level and VTE1gene expression.

Accurate determination of total biophenols in unfractionated extra-virgin olive oil with the fast blue BB assay

The phenolic compounds of extra-virgin olive oil (EVOO) are key contributors of nutritional and sensory quality as well as chemical stability. The reference method for their determination is the HPLC-UV, which is cost-/time-expensive. In this work, total phenolic compounds were evaluated in unfractionated EVOO adapting the Fast Blue BB (FBBB) assay, which involves the spectrophotometric (absorbance at 420 nm) determination of azo derivatives resulting from the coupling of phenolic compounds with FBBB diazonium salt in alkali pH. When tested on 26 EVOO samples, the FBBB assay and HPLC-determinations were strikingly correlated (R² = 0.9653), differently from FBBB and Folin-Ciocalteu assays, which showed poor correlation. The assay is simple, repeatable, robust, rapid and cheap, and results might be evaluated on a printed colorimetric scale. This protocol of the FBBB assay could be routinely used to categorize EVOO according to the health claim allowed by EFSA concerning the content of phenolic compounds.

Effect of fruit shading and cold storage on tocopherol biosynthesis and its involvement in the susceptibility of Star Ruby grapefruit to chilling injury

•

Tocopherol content in the flavedo of grapefruit increase during fruit maturation.

•

TAT1 and genes of the tocopherol-core pathway are up-regulated during fruit maturation.

•

Light avoidance reduces γ-tocopherol and expression of GGDR and tocopherol-core pathway genes.

•

Cold up-regulated genes involved in precursors supply but repressed those of the core pathway.

•

Changes in tocopherols during storage appears to be cold-mediated and not related to CI tolerance.

The aim of this study was to investigate the role of tocopherols in the susceptibility of Star Ruby grapefruit to postharvest chilling injury (CI). Fruit exposed to normal sunlight (NC, non-covered) and deprived of light (C, covered) in the last stages of development were used. Tocopherol contents increased in the flavedo of both NC and C fruit during development, concomitantly with the up-regulation of TAT1 and most genes of the tocopherol-core pathway. Fruit shading reduced total contents by repressing γ-tocopherol accumulation, associated to a down-regulation of GGDR and VTE1 and, to a lesser extent, of VTE2, VTE3a and VTE4. During cold storage, total and α-tocopherol contents increased in NC and C fruit, and no direct relationship between tocopherol accumulation and CI tolerance was found. Cold stress up-regulated most genes involved in the synthesis of tocopherol precursors and down-regulated those of the tocopherol-core pathway, but changes seemed to be cold-mediated and not related to CI development.

Regulation of Tocopherol Biosynthesis During Fruit Maturation of Different Citrus Species

Tocopherols are plant-derived isoprenoids with vitamin E activity, which are involved in diverse physiological processes in plants. Although their biosynthesis has been extensively investigated in model plants, their synthesis in important fruit crops as Citrus has scarcely been studied. Therefore, the aim of this work was to initiate a physiological and molecular characterization of tocopherol synthesis and accumulation in Citrus fruits during maturation. For that purpose, we selected fruit of the four main commercial species: grapefruit (Citrus paradisi), lemon (Citrus limon), sweet orange (Citrus sinensis), and mandarin (Citrus clementina), and analyzed tocopherol content and the expression profile of 14 genes involved in tocopherol synthesis during fruit maturation in both the flavedo and pulp. The selected genes covered the pathways supplying the tocopherol precursors homogentisate (HGA) (TAT1 and HPPD) and phytyl pyrophosphate (PPP) (VTE5, VTE6, DXS1 and 2, GGPPS1 and 6, and GGDR) and the tocopherol-core pathway (VTE2, VTE3a, VTE3b, VTE1, and VTE4). Tocopherols accumulated mainly as α- and γ-tocopherol, and α-tocopherol was the predominant form in both tissues. Moreover, differences were detected between tissues, among maturation stages and genotypes. Contents were higher in the flavedo than in the pulp during maturation, and while they increased in the flavedo they decreased or were maintained in the pulp. Among genotypes, mature fruit of lemon accumulated the highest tocopherol content in both the flavedo and the pulp, whereas mandarin fruit accumulated the lowest concentrations, and grapefruit and orange had intermediate levels. Higher concentrations in the flavedo were associated with a higher expression of all the genes evaluated, and different genes are suitable candidates to explain the temporal changes in each tissue: (1) in the flavedo, the increase in tocopherols was concomitant with the up-regulation of TAT1 and VTE4, involved in the supply of HGA and the shift of γ- into α-tocopherol, respectively; and (2) in the pulp, changes paralleled the expression of VTE6, DXS2, and GGDR, which regulate PPP availability. Also, certain genes (i.e., VTE6, DXS2, and GGDR) were co-regulated and shared a similar pattern during maturation in both tissues, suggesting they are developmentally modulated.

Effect of olive ripening degree on the antidiabetic potential of biophenols-rich extracts of Brava Gallega virgin olive oils

The diet management is imperative to anticipate risk factors that favour the development of diseases; indeed, the intake of virgin olive oil could be an alternative natural source of α-glucosidase enzyme inhibitors, which delay the digestion rate of carbohydrates. Consequently, the impact of diabetes mellitus (DM) could be diminished. Extra Virgin Olive Oils (EVOO) were elaborated from Galician autochthonous variety 'Brava Gallega' with olives selected at three different degree of ripeness (ripening index, RI: 1.4, 3.0, 5.5) in order to assess the effect of maturation on overall chemical composition, sensory quality, and enzyme inhibition. The phenolic profile of the EVOOs determined by LC-ESI-IT-MS exhibited quantitative differences as ripening advanced; for example oleocanthal, tyrosol, luteolin and apigenin concentrations were higher in the overripe olive oil (RI 5.5). Anyway, the phenolic extracts (from every tested RI) were more active than acarbose. In particular, those obtained from the most mature olives displayed the most powerful inhibitory activity (IC₅₀ value of 143 µg of dry extract/mL). In addition, the significant effect of these compounds (i.e. luteolin, apigenin, tyrosol and oleocanthal) on the inhibitory activity of the olive oil extracts was demonstrated. Our results suggest that, regardless of RI, the inhibitory activity of 'Brava Gallega' olive oils could represent a valuable strategy for reinforcing the health claim of olive oil for phenolic compounds.

Analysis of Olive (Olea Europaea L.) Genetic Resources in Relation to the Content of Vitamin E in Virgin Olive Oil

Virgin olive oil (VOO) is the main source of lipids in the Mediterranean diet and one of the main contributors to its proven protection against diseases associated with chronic inflammation states. This oil is rich in antioxidant compounds such as tocopherols, which together constitute the vitamin E stock of the oil. The purpose of the present work was to conduct a study on the diversity of the contents of vitamin E in the olive species (Olea europaea L.), and to know how the season climatic conditions and the degree of fruit ripening stage influences the final content of this vitamin in VOO. Data showed that the content of vitamin E in VOO is highly dependent on the olive cultivar, displaying a wide variability (89–1410 mg tocopherol/kg oil) in the olive species, and that is also dependent, to a lesser extent, on the crop year climate and the stage of fruit ripening. In addition, the suitability of cultivar crosses for breeding programs to obtain new cultivars with improved vitamin E content in VOO has been assessed. Our findings demonstrated that a single cross of olive cultivars may provide sufficient variability to be used in the selection of new cultivars.