Transgenic Approach to Improve Quality Traits of Melon Fruit
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Scientia Horticulturae 108 (2006) 268–277 www.elsevier.com/locate/scihorti Transgenic approach to improve quality traits of melon fruit Zhengguo Li a,*, Lihu Yao b, Yingwu Yang a, Aidong Li a a Genetic Engineering Research Center, Chongqing University, Chongqing 400030, China b Imperial Flavours Inc., Mississauga, Ont., Canada L4T 3L8 Received 31 January 2005; received in revised form 12 January 2006; accepted 2 February 2006 Abstract Melon is one of the economically important and widely cultivated vegetable crops in the world. There is a wide genetic diversity in the cultivated and wild species of melon. Melon as one of the most consumed fruits, the development and ripening of fruit is known to be a complex developmental process that involves many biochemical and physiological changes including the breakdown of chlorophyll, degradation of the cell wall, increase in sugars content, alteration in pigment biosynthesis, and the accumulation of flavour and aromatic compounds. However, the information on genetic engineering and molecular biology of melon is very limited. With the development of genetics and molecular biology, a large number of quality/ripening-regulated genes involved in pigmentation, vitamin, soluble carbohydrate metabolism, cell wall metabolism and ethylene biosynthesis have been identified in melons. Some genetic manipulations of melons have been proved to be useful technology to improve quality, sensory attributes, shelf life and other agronomic traits of melon fruit. This paper reviewed some progresses in the trangenic approach to improve quality traits of melon fruit. # 2006 Elsevier B.V. All rights reserved. Keywords: Melon (Cucumis melo L.); Genetic engineering; Fruit; Quality trait; Ethylene 1. Introduction of the genes underlying the phenotypic variation observed in melon germplasm. Melon (Cucumis melo L.), an African-originated annual Melon as one of the most consumed fruits, such as orange- diploid plant (2n =2x = 24), is one of the economically flesh cantaloupe melons and green-flesh honeydew melons important and widely cultivated crops in the world. It is the provide pro-vitamin A (b-carotene) and C, and a number of most morphologically diverse species in the genus Cucumis nutrients, such as vitamin E and folic acid in the daily dietary (Kirkbride, 1993), and differs widely in fruit size, morphology (Table 1). These nutrients are known as strong antioxidants and and taste, as well as vegetative traits and climatic adaptation important compounds in human metabolic reactions. (Silberstein et al., 2003). Fruits of C. melo exhibit a wide range Melon fruit quality is a combination of a number of of morphological variation, including fruits from a few grams to biochemical and developmental processes that result in several kilograms, climacteric to non-climacteric, oblong to changes in colour, texture, flavour, and aroma of the fruit. very elongated shapes or flesh taste from bitter to very sweet Traditional breeding and cultivation techniques have con- (Kirkbride, 1993; Stepansky et al., 1999; Liu et al., 2004; tributed significantly to improved fruit quality of melon. Monforte et al., 2004). Over 160 major genes controlling Transgenic technology has been demonstrated the potential to different aspects of melon biology have been described (Pitrat, increase yields even more and will enable the development of 2002). Some molecular markers and reference maps of C. melo plants that can grow under less favourable conditions; it might are available (Perin et al., 2002a,b; Gonzalo et al., 2005). But be possible to engineer plants that are more resistant to these mapped genes should represent only a very small fraction pathogens or insects and that can be better quality and maintained during transport. Transgenic technology could also significantly improve the content of functional compo- nents in some plants (Uzogara, 2000). As the development of * Corresponding author at: 174# Shazheng Road, Shapingba District, Genetic knowledge of melon genomics and possible genetic trans- Engineering Research Center, Chongqing University, Chongqing 400030, China. Tel.: +86 23 6512 0483; fax: +86 23 6512 0490. formation through Agrobacterium tumefaciens (Ayub et al., E-mail address: [email protected] (Z. Li). 1996), a large number of quality/ripening-regulated genes 0304-4238/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.scienta.2006.02.005 Z. Li et al. / Scientia Horticulturae 108 (2006) 268–277 269 Table 1 2. Control of ethylene biosynthesis and action Nutritional compositions of cantaloupe and honeydew melons (value per 100 g of edible portion) Ethylene is an endogenous plant hormone that affects many Composition Cantaloupe Honeydew aspects of a plant in its growth, development, fruit ripening Overall composition (including shelf life, shipping potential, storage behavior, and Water (g) 89.78 89.66 quality of fruits), and responses to stress (Abeles et al., 1992; Minerals (g) 0.36 0.34 Adams-Phillips et al., 2004). Ethylene biosynthetic, from S- Proteins (g) 0.88 0.46 adenosylmethionine (AdoMet) through the intermediate 1- Total lipid (g) 0.28 0.10 Carbohydrate (g) 8.36 9.18 aminocyclopropane-1-carboxylic acid (ACC), is controlled by Fibre, total dietary (g) 0.8 0.6 ACC synthase (ACS) that catalyzes the conversion of S- Ash (g) 0.71 0.60 adenosylmethionine to ACC, and ACC oxidase (ACO) that Vitamins catalyzes the conversion of ACC to ethylene (Yang and Vitamin A (IU) 3224 40 Hoffman, 1984). Ethylene binding to receptors with homology Vitamin C (mg) 42.2 24.8 to two-component regulators triggers a kinase cascade that is Thiamin (mg) 0.036 0.077 propagated through the CTR1 Raf-like kinase and other Riboflavin (mg) 0.021 0.018 Niacin (mg) 0.574 0.600 components to the nucleus. Activation of the EIN3 family of Pantothenic acid (mg) 0.128 0.207 nuclear proteins leads to an induction of the relevant ethylene- Vitamin B6 (mg) 0.115 0.059 responsive genes via other transcription factors, eliciting a Vitamin E (tocopherol, alpha) (mg) 0.14 0.14 response to appropriate to the original stimulus (Johnson and From USDA Nutrient Database, July 2001. Ecker, 1998). Ethylene plays a major role in the ripening of climacteric fruit and some varieties of melon. The sharp increase in involving in pigmentation, soluble carbohydrate metabolism, ethylene production at the onset of ripening has been thought of and cell wall metabolism and ethylene biosynthesis have been a cause for the changes in sweetness, colour, aroma, texture and identifiedinmelon(Table 2, Pitrat, 2002). The function of flavour from immature solid fruit to ripen fruit, which makes some ripening-regulated genes has been studied through the fruit acceptable and ready for consumption (Giovannoni, altering their expressions in transgenic plants (Ayub et al., 2001; Adams-Phillips et al., 2004). In most of melon varieties, 1996). It will provide scientists with the information needed ethylene production was positively significantly correlated with to apply transgenic techniques more successfully, when postharvest decay rating. Orange-fleshed melon fruits produced applied appropriately. The isolation and expression of these more ethylene than green- or white-fleshed types. Melon fruits genes in transgenic plants offer therefore a potential to with a netted rind had higher ethylene production than smooth- improve fruit quality and shelf life by altering metabolism type fruits (Zheng and Wolff, 2000). Genetic manipulation of pathways through biotechnological methods. Furthermore, ethylene production could be a measure to control climacteric molecular transgenic research will also provide information fruit ripening. Ethylene production is regulated at multiple on how to melon in such a way that certain properties, like levels, from hormone synthesis and perception to signal flavours, nutrition and functional components, are simulta- transduction and transcription. As more genes in the ethylene neously optimised. biosynthesis and response pathways have been cloned and Table 2 Some quality/ripening-regulated genes isolated from melon Gene Function Reference CMe-ACS1, CMe-ACS2, CMe-ACS3, ACC synthase Yamamoto et al. (1995), Ishiki CMe-ACS4, and CMe-ACS5 et al. (2000), Miki et al. (1995), Li et al. (unpublished) CMe-ACO1, CMe-ACO2, and CMe-ACO3 ACC oxydase Lasserre et al. (1996), Guis et al. (1997b) CM-ERS1, CM-ETR1 Ethylene receptor Sato-Nara et al. (1999), Takahashi et al. (2002) CMe-EIN3 Transcription factor Li et al. (unpublished) MEL5 Phytoene synthase Karvouni et al. (1995) MPG1, MPG2, and MPG3 Polygalacturonase Hadfield et al. (1998b) CM-AAT1 and CM-AAT2 Alcohol acetyltransferases Yahyaoui et al. (2002) Mao1, Mao2, and Mao3 Ascorbate oxidase Diallinas et al. (1997) CmGalLDH L-Galactono-1,4-lactone dehydrogenase Pateraki et al. (2004) pmPAL-1 Phenylalanine ammonia-lyase Diallinas and Kanellis (1994) Cmf-25 Extensin-like protein Choi et al. (2003) Cmf-30 Seed nucecllus-specific protein Choi et al. (2003) 270 Z. Li et al. / Scientia Horticulturae 108 (2006) 268–277 characterized, ethylene production and signal transduction can melons are typical climacteric orange-fleshed melons that be controlled precisely (Johnson and Ecker, 1998). Reducing exhibit good sensory attributes but have short shelf life. It has ethylene biosynthesis and action may be a measure to slow become the second fruit after tomato for the genetic down the post harvest deterioration of fruits and hence to limit manipulation to control ethylene production when high postharvest losses and extend