Grape Berry Transcriptome

Fruit development and ripening is a complex and fascinating phenomenon unique to plants. Fruits are organs specialized for seed dispersal, and the transition from unripe fruit, which must be protected against damage caused by animals, to ripe fruit, which must be made appealing to the same animals in order to facilitate seed dispersal, is a key reproductive strategy for plants. Ripening can generally be described as the coordinated manifestation of changes in colour, texture, flavour, aroma, and nutritional characteristics, which make fruits attractive (Giovannoni, 2001). Fleshy fruits make up a large proportion of the human diet, so the development and ripening process has received considerable scientific attention. Tomato, banana, apple, pear and most stone fruit species yield climacteric fruits, characterized by a respiration burst at the onset of ripening followed by the accumulation of ethylene. Neither of these events is necessary for the ripening of non-climacteric fruits, which include strawberries, citrus and grape berries (Seymour et al., 2013). Grapevine (Vitis vinifera L.) is one the oldest and most widely-cultivated perennial fruit crops in the world. The economic value of this species reflects the high quality attributes of its ripe berries, which are rich in sugars and secondary metabolites, including anthocyanins, tannins, carotenoids, norisoprenoids, terpenes and other volatile organic compounds. Grapes offer a wealth of health benefits due to their high nutrient and antioxidant contents. Grapes are high in a number of powerful antioxidant compounds. In fact, over 1600 beneficial plant compounds have been identified in this fruit. Most of the research on grapes has been done on seed or skin extracts because the highest concentration of antioxidants has been documented in these organs. In particular, red grapes contain higher numbers of antioxidants due to the anthocyanins that give them their color and red wine is also high in these compound because the antioxidants in grapes remain present even after fermentation. One of the most prevalent antioxidants in grape is resveratrol, which is classified as a polyphenol. Grapes also contain vitamin C, beta-carotene, quercetin, lutein, lycopene and ellagic acid, which are powerful antioxidants as well. Grapevine has a strong, ancient connection with human culture and civilization. The modern grapevine (V. vinifera sbs. sativa) was domesticated 8000 years ago in the Southern Caucasus region (McGovern, 2003) from its wild ancestor V. vinifera sbs. sylvestris. There are currently 5,000–10,000 varieties, although few are commercially significant for wine and table grape production (Alleweldt and Dettweiler-Munch, 1992) and breeding is restricted to a relatively small number of cultivars, mostly producing grapes for fresh consumption. The agronomic and phenotypic characterization of hundreds of varieties grown for many years has revealed immense genotypic diversity and significant phenotypic plasticity, i.e. the ability to express different phenotypes from the same base genotype depending on the cultivation environment (McIntyre et al., 1982; Bouriquot et al., 1995; Tomasi et al., 2011). This has facilitated the global spread of grapevine to many different climatic regions. Grapes are grown mainly in temperate climates across the world, including Southern Europe, Africa, Australia and North and South America. The majority of grapes grown in the US are from California. The grapevine genome is highly polymorphic (Lijavetzky et al., 2007) and vegetative propagation is preferred over seed germination because extensive heterozygosity results in erratic yields and produces offspring with diverse characteristics (Forneck et al., 2009). However, the global demand for high-quality wines is increasing, awakening interest in the use of local cultivars to create premium products and in the molecular analysis of their prized organoleptic traits (Bisson et al., 2002).