Genetic Control of Fruit Vitamin C Contents

Abstract

An F 1 progeny derived from a cross between the apple (Malus x domestica) cultivars Telamon and Braeburn was used to identify quantitative trait loci (QTL) linked to the vitamin C (L-ascorbate [L-AA]) contents of fruit skin and flesh (cortex) tissues. We identified up to three highly significant QTLs for both the mean L-AA and the mean total L-AA contents of fruit flesh on both parental genetic linkage maps, confirming the quantitative nature of these traits. These QTLs account for up to a maximum of 60% of the total population variation observed in the progeny, and with a maximal individual contribution of 31% per QTL. QTLs common to both parents were identified on linkage groups (LGs) 6, 10, and 11 of the Malus reference map, while each parent also had additional unique QTLs on other LGs. Interestingly, one strong QTL on LG-17 of the Telamon linkage map colocalized with a highly significant QTL associated with flesh browning, and a minor QTL for dehydroascorbate content, supporting earlier work that links fruit L-AA contents with the susceptibility of hardfruit to postharvest browning. We also found significant minor QTLs for skin L-AA and total L-AA (L-AA 1 dehydroascorbate) contents in Telamon. Currently, little is known about the genetic determinants underlying tissue L-AA homeostasis, but the presence of major, highly significant QTL in both these apple genotypes under field conditions suggests the existence of common control mechanisms, allelic heterozygosity, and helps outline strategies and the potential for the molecular breeding of these traits.Vitamin C (L-ascorbic acid [L-AA]) is essential for all living plant tissues. Apart from well-known functions in oxidative stress defense, associated with its antioxidant properties and its abilities to detoxify reactive oxygen species, it also has important roles in the regulation of plant cell growth and expansion, photosynthesis, as well as hormone functions (for review, see Davey et al., 2000;Smirnoff, 2000). Even though nutritional deficiencies are rare in modern western cultures, it is generally recognized that dietary L-AA also has important health benefits for the consumer, and an increased intake of vitamin C has been associated with a decreased incidence of several important human diseases and disorders (Carr and Frei, 1999; DemmigAdams and Adams, 2002;Hancock and Viola, 2005). Furthermore, in meat-poor diets, dietary L-AA can contribute to the improved uptake of iron and zinc, which are the major micronutrient deficiencies worldwide (Frossard et al., 2000). In apple (Malus x domestica) and other fruit species, there are indications that increased antioxidant contents and in particular higher L-AA levels may be associated with improved fruit postharvest properties (Barden and Bramlage, 1994;Veltman et al., 1999Muckenschnabel et al., 2001;Venisse et al., 2001;Franck et al., 2003aFranck et al., , 2003bHodges et al., 2004;Hancock and Viola, 2005). In addition, L-AA has been implicated in resistance to a wide range of biotic and abiotic stresses (Davey ...

Allelic Variation in Paralogs of GDP-l-Galactose Phosphorylase Is a Major Determinant of Vitamin C Concentrations in Apple Fruit

“…Links between Vitamin C Concentrations, Flesh Browning, and Other Fruit Quality Traits Susceptibility to browning has been linked to flesh DHA concentrations in apple (Davey et al, 2006), and in pears, the development of internal postharvest browning disorder occurs when AsA concentrations decline below a certain threshold value (Franck et al, 2003). Here, the time taken for cut apple flesh to complete browning and the final color intensity following browning were both correlated with DHA concentrations and the percentage DHA of flesh tissues.…”

“…Ripeness was assessed by experts based on ripening parameters. A minimum of 10 healthy apples per genotype were sampled for AsA, totAsA, GSH, totGSH, and TAA analysis and processed essentially as described previously (Davey et al, 2006). Fruit were immediately transported to the laboratory for analysis.…”

“…Samples for metabolite analysis were obtained from skin and flesh fractions from 10 individual fruit by blending using a metaphosphoric acid/EDTA/ polyvinylpolypyrrolidone extraction, essentially as described previously (Davey et al, , 2006. Extracts were filtered and injected into an HPLC system (Waters 2690 separation module) equipped with a C 18 rocket column (Grace; 53 mm 3 7 mm).…”

“…In addition to these antioxidant functions, AsA has been shown to be involved in a range of important cellular processes, including plant development and hormone signaling, cell cycle, cell expansion, senescence, and as a cofactor for a number of important enzymes (for review, see Davey et al, 2000;Smirnoff et al, 2001;Noctor, 2006). Fruit AsA concentrations have also been correlated with the maintenance of quality during postharvest storage Davey et al, 2007) and have been linked to susceptibility to internal browning in both apple (Malus 3 domestica; Davey et al, 2006;Davey and Keulemans, 2009) and pear (Pyrus communis; Veltman et al, 1999;Franck et al, 2003). Finally, AsA is clearly an essential dietary component for humans, with a protective role proposed for many disorders and diseases (Diplock et al, 1998).…”

“…Initial quantitative trait loci (QTL) analyses of AsA concentrations (Davey et al, 2006) have been expanded to identify QTL for other antioxidants and fruit quality traits over three years, including results in 1 year comparing the concentrations of AsA in fruit and leaves. Alignments of the apple orthologs of genes involved in AsA biosynthesis, turnover, and transport against the whole genome sequence of cv Golden Delicious (Velasco et al, 2010) allowed us to identify candidate genes (CGs) colocating with stable QTL clusters.…”