Temporal analysis reveals a key role for VTE5 in vitamin E biosynthesis in olive fruit during on-tree development

Abstract

The aim of this work was to generate a high resolution temporal mapping of the biosynthetic pathway of vitamin E in olive fruit (Olea europaea cv. “Koroneiki”) during 17 successive on-tree developmental stages. Fruit material was collected from the middle of June until the end of January, corresponding to 6–38 weeks after flowering (WAF). Results revealed a variable gene regulation pattern among 6–38 WAF studied and more pronounced levels of differential regulation of gene expression for the first and intermediate genes in the biosynthetic pathway (VTE5, geranylgeranyl reductase, HPPD, VTE2, HGGT and VTE3) compared with the downstream components of the pathway (VTE1 and VTE4). Notably, expression of HGGT and VTE2 genes were significantly suppressed throughout the developmental stages examined. Metabolite analysis indicated that the first and intermediate stages of development (6–22 WAF) have higher concentrations of tocochromanols compared with the last on-tree stages (starting from 24 WAF onwards). The concentration of α-tocopherol (16.15 ± 0.60−32.45 ± 0.54 mg/100 g F.W.) were substantially greater (up to 100-fold) than those of β-, γ-, and δ-tocopherols (0.13 ± 0.01−0.25 ± 0.03 mg/100 g F.W., 0.13 ± 0.01−0.33 ± 0.04 mg/100 g F.W., 0.14 ± 0.01−0.28 ± 0.01 mg/100 g F.W., respectively). In regard with tocotrienol content, only γ-tocotrienol was detected. Overall, olive fruits (cv. “Koroneiki”) exhibited higher concentrations of vitamin E until 22 WAF as compared with later WAF, concomitant with the expression profile of phytol kinase (VTE5), which could be used as a marker gene due to its importance in the biosynthesis of vitamin E. To the best of our knowledge, this is the first study that explores the complete biosynthetic pathway of vitamin E in a fruit tree crop of great horticultural importance such as olive, linking molecular gene expression analysis with tocochromanol content.

Molecular characterization of tocopherol biosynthesisgenes from Olea europaea (L.) cv. Ayvalık

“…Our results showed that the α-tocopherol content of the Ayvalık cultivar was between 26.78 and 21.05 mg/100 g, with the highest levels noted for the 21 October samples. The results from the Koroneiki cultivar revealed similar values within the same stages of maturation (Georgiadou et al, 2015). Both cultivars exhibited increased α-tocopherol content at early stages of maturation.…”

“…Although it is known that ethylene levels increase throughout the fruit ripening process (Lelievre et al, 1997), tocopherol levels exhibit different patterns in different olive cultivars. Although Hojiblanca (Beltran et al, 2005) and Koroneiki (Georgiadou et al, 2015) exhibited an increase, Verdial and Villalonga (Garcia et al, 1996) exhibited a decrease in α-tocopherol content. In addition, the arbequina and lechin (Garcia et al, 1996) cultivars did not exhibit significant changes.…”

“…Although OeVTE3, OeVTE1, and OeGTMT expression was increased in the 7 October samples among the five sample groups, we did not identify any statistically significant change in later samples (21 October, 4 November, 18 November, 2 December). A recent study revealed expression levels of tocopherol biosynthesis genes and tocopherol content in the Koroneiki olive cultivar (Georgiadou et al, 2015). The authors found that the expression levels of GTMT were increased before fruit coloring but reduced during later stages, such as fruit coloring and harvest maturity.…”

“…Genes involved in tocopherol biosynthesis were previously characterized in different model organisms (DellaPenna and Pogson, 2006;Quadrana et al, 2013), and recent studies revealed an association between tocopherol content and expression levels of genes involved in tocopherol biosynthesis (Georgiadou et al, 2015). In this paper, we present full-length cloning and bioinformatic analysis of five olive genes involved in tocopherol biosynthesis for the first time.…”

Comparative analysis of minor bioactive constituents (CoQ10, tocopherols and phenolic compounds) in Arbequina extra virgin olive oils from Brazil and Spain

“…In this sense, increasing the tocopherol content could be an auto-protection mechanism of plants against some stress conditions, such as water stress (Beltrán et al, 2010). However, there is a maximum level depending on the fruit development (Georgiadou et al, 2015). In this line, our results show that climate factors are linked to tocopherols content and may impact them, but the influence of other factors providing synergic or antagonist effects, as the maturation index, cannot be discarded.…”