Consuming functional foods such as fruit and vegetables are important for reducing the risk of chronic diseases and maintaining good health. At least five to nine daily servings of fruits and vegetables are recommended by the U.S. Department of Agriculture (Zepeda et al., 2014). Fruit and vegetables provide essential vitamins, minerals, fibers (soluble and insoluble forms) as well as bioactive compounds collectively known as phytochemicals. These include polyphenols, carotenoids, and sulfur-containing components. In addition to health benefits, diversity in fruit colors is often associated with unique phytochemical constituents (Camara et al., 1995; Gould et al., 2010; Tzulker et al., 2007). Among several fruit in the Rosaceae family, european plum provide enormous amount of phytonutrients due to their high polyphenolic and fiber content thus constituting a functional health food.
Fruit color is a primary attribute to the appearance and quality of european plum. In general, color is important in attraction of dispersal agents (birds, animals, and primates), protection against ultraviolet damage, an indicator of ripeness, and contributes to polyphenolic content and their associated antioxidant properties (Davies and Schwinn, 2004). As the fruit ripens, color is one of many modifications that occur due to physiological and biochemical changes; including the increase in respiration rate, production of ethylene, flesh softening, and formation of volatiles with associated development of flavor. During the ripening of european plum, there is loss of chlorophyll pigment that leads to development of blue-black, purple, or yellow pigmentation (Abdi et al., 1998). In higher plants these pigments are localized in chromoplasts or vacuoles (Kahlau and Bock, 2008). The compounds responsible for this diverse pigmentation are anthocyanins synthesized through a specific biosynthetic pathway in most plants, including european plum.
Anthocyanin pathway includes an early biosynthetic pathway that leads to the production of colorless dihydroflavonol compounds and late biosynthetic pathway that leads to the production of anthocyanins (color pigmentation) (Holton and Cornish, 1995; Jaakola et al., 2002). The activity of ABGs is believed to be crucial in the formation of anthocyanins with different structure and coloration including conjugates of cyanidin (red), pelargonidin (orange), and delphindin (blue) (Dooner et al., 1991). The expression of the ABGs depends on several factors; including tissue, genotype, developmental stage, and environment (Boss et al., 1996; Takos et al., 2006); and may serve as qualitative and quantitative indicator of pigmentation in ripe fruit. Molecular mechanisms underlying the regulation of anthocyanin biosynthetic pathway have been investigated in some species, such as grape (Vitis vinifera), bilberry (Vaccinium myrtillus), and malay apple (Syzygium malaccense), but not well understood in the case of european plum (Fournand et al., 2006; Jaakola et al., 2002; Kotepong et al., 2011).
In the present study, european plum genotypes with varied fruit colors ranging from green to purple were used as a model system to better understand the role of anthocyanin biosynthetic pathway in the regulation of european plum pigmentation at ripening. The expression of key ABGs was assessed during european plum fruit ripening and the functional analysis of individual ABG was examined using tobacco as a heterologous experimental system. The findings of this research can be used in breeding programs aiming at obtaining european plum with desired colors for the market and consumers.
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Primers used for gene expression analysis of anthocyanin biosynthetic genes in european plum genotypes.
Accession numbers of anthocyanin biosynthetic genes from european plum.
Primers used for the isolation of anthocyanin biosynthetic genes from european plum.
Primers used for the genetic transformation of anthocyanin biosynthetic genes (ABG) and to examine the presence of ABG in transgenic tobacco plants.
Total polyphenol content of different colored cultivars of european plum eluted in 100% methanol fraction.
Liquid chromatography–mass spectrometry profile of polyphenols from the european plum purple genotype V982017.
Liquid chromatography–mass spectrometry profile of polyphenols from the european plum greenish-purple genotype V90271.
Liquid chromatography–mass spectrometry profile of polyphenols from the european plum yellow 1 genotype V91058.
Liquid chromatography–mass spectrometry profile of polyphenols from the european plum yellow 2 genotype V91057.
Liquid chromatography–mass spectrometry profile of polyphenols from the european plum green 1 genotype V91048.
Liquid chromatography–mass spectrometry profile of polyphenols from the european plum green 2 genotye V91057.