Abstract
Litchi has diverse fruit color phenotypes, yet no research reflects the biochemical background of this diversity. In this study, we evaluated 12 litchi cultivars for chromatic parameters and pigments, and investigated the effects of abscisic acid, forchlorofenron (CPPU), bagging and debagging treatments on fruit coloration in cv. Feizixiao, an unevenly red cultivar. Six genes encoding chalcone synthase (CHS), chalcone isomerase (CHI), flavanone 3-hydroxylase (F3H), dihydroflavonol 4-reductase (DFR), anthocyanidin synthase (ANS) and UDP-glucose: flavonoid 3-O-glucosyltransferase (UFGT) were isolated from the pericarp of the fully red litchi cv. Nuomici, and their expression was analyzed in different cultivars and under the above mentioned treatments. Pericarp anthocyanin concentration varied from none to 734 mg m−2 among the 12 litchi cultivars, which were divided into three coloration types, i.e. non-red (‘Kuixingqingpitian’, ‘Xingqiumili’, ‘Yamulong’and ‘Yongxing No. 2′), unevenly red (‘Feizixiao’ and ‘Sanyuehong’) and fully red (‘Meiguili’, ‘Baila’, Baitangying’ ’Guiwei’, ‘Nuomici’ and ‘Guinuo’). The fully red type cultivars had different levels of anthocyanin but with the same composition. The expression of the six genes, especially LcF3H, LcDFR, LcANS and LcUFGT, in the pericarp of non-red cultivars was much weaker as compared to those red cultivars. Their expression, LcDFR and LcUFGT in particular, was positively correlated with anthocyanin concentrations in the pericarp. These results suggest the late genes in the anthocyanin biosynthetic pathway were coordinately expressed during red coloration of litchi fruits. Low expression of these genes resulted in absence or extremely low anthocyanin accumulation in non-red cultivars. Zero-red pericarp from either immature or CPPU treated fruits appeared to be lacking in anthocyanins due to the absence of UFGT expression. Among these six genes, only the expression of UFGT was found significantly correlated with the pericarp anthocyanin concentration (r = 0.84). These results suggest that UFGT played a predominant role in the anthocyanin accumulation in litchi as well as pericarp coloration of a given cultivar.
Highlights
Pigmentation is an appealing feature of fruits
The early sections leads to the formation of the dihydro-flavonols, comprising phenylalanine ammonialyase (PAL), cinnimate 4-hydroxylase (C4H), 4coumarate: CoA ligase (4CL), chalcone synthase (CHS), chalcone isomerase (CHI), and flavanone 3-hydroxylase (F3H)
We demonstrated that a wide range of variability among litchi cultivars in their concentrations of anthocyanins and chlorophylls and chromatic parameters at fruit maturity (Table 1, Fig. 2)
Summary
Pigmentation is an appealing feature of fruits. Among the four pigment groups, i.e. anthocyanins, betalains, chlorophylls and carotenoids, anthocyanins are the most prominent imparting red, blue and black hues to the fruits in which they accumulate [1].Anthocyanin biosynthesis is probably the most thoroughly studied plant secondary metabolism pathway. Pigmentation is an appealing feature of fruits. The metabolic pathway leading to their production has been well characterised in some model plants [2] This pathway is usually divided into two sections, the early and the late sections [3]. The early sections leads to the formation of the dihydro-flavonols, comprising phenylalanine ammonialyase (PAL), cinnimate 4-hydroxylase (C4H), 4coumarate: CoA ligase (4CL), chalcone synthase (CHS), chalcone isomerase (CHI), and flavanone 3-hydroxylase (F3H). Genes of these enzymes in the early section are here called the early genes. Genes expressing the three enzymes are called the late genes in anthocyanin biosynthesis
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