RETRACTED ARTICLE: Contribution of anthocyanin pathways to fruit flesh coloration in pitayas

Abstract

Background: Color formation in Hylocereus spp. (pitayas) has been ascribed to the accumulation of betalains. However, several studies have reported the presence of anthocyanins in pitaya fruit and their potential role in color formation has not yet been explored. In this study, we profiled metabolome and transcriptome in fruit of three cultivars with contrasting flesh colors (red, pink and white) to investigate their nutritional quality and the mechanism of color formation involving anthocyanins. Results: Results revealed that pitaya fruit is enriched in amino acid, lipid, carbohydrate, polyphenols, vitamin and other bioactive components with significant variation among the three cultivars. Anthocyanins were detected in the fruit flesh and accumulation levels of Cyanidin 3-glucoside, Cyanidin 3-rutinoside, Delphinidin 3-O-(6-Omalonyl)-beta-glucoside-3-O-beta-glucoside and Delphinidin 3-O-beta-D-glucoside 5-O-(6-coumaroyl-beta-Dglucoside) positively correlated with the reddish coloration. Transcriptome data showed that the white cultivar tends to repress the anthocyanin biosynthetic pathway and divert substrates to other competing pathways. This perfectly contrasted with observations in the red cultivar. The pink cultivar however seems to keep a balance between the anthocyanin biosynthetic pathway and the competing pathways. We identified several active transcription factors of the MYB and bHLH families which can be further investigated as potential regulators of the anthocyanin biosynthetic genes. Conclusions: Collectively, our results suggest that anthocyanins partly contribute to color formation in pitaya fruit. Future studies aiming at manipulating the biosynthetic pathways of anthocyanins and betalains will better clarify the exact contribution of each pathway in color formation in pitayas. This will facilitate efforts to improve pitaya fruit quality and appeal.

Unraveling the Regulatory Mechanism of Color Diversity in Camellia japonica Petals by Integrative Transcriptome and Metabolome Analysis

“…Anthocyanins also contribute to fruit color, such as in Hylocereus spp. (Fan et al, 2020) and Morus atropurpurea (Huang et al, 2020). Moreover, anthocyanin has various other functions in plants, including in the protection against abiotic stresses, resistance to pathogens, tolerance to environmental stresses, and pollinator attraction (Schaefer et al, 2004;Zhang et al, 2015).…”

The report of anthocyanins in the betalain-pigmented genus Hylocereus is not well evidenced and is not a strong basis to refute the mutual exclusion paradigm

“…Fan et al [ 9 ] did not report the detection of betalains in the fruits of Hylocereus cultivars in their analyses. But as cited by Fan et al [ 9 ], a range of betalain pigments have previously been detected by numerous studies in the same species [ 10 – 14 ].…”

“…With this as context, Fan et al [ 9 ] recently reported anthocyanins within the betalain-pigmented genus Hylocereus (Cactaceae), also commonly called Pitaya. Fan et al [ 9 ] analysed the fruits of three closely related species – a red-fleshed Hylocereus polyrhizus, a white-fleshed Hylocereus undatus , and an intermediate pink-fleshed hybrid ( H. polyrhizus x H. undatus ). Based on the analysis, they reported to correlate the accumulation of anthocyanins with the colour of red and pink fruit pulps, and the expression levels of anthocyanin biosynthesis genes.…”

“…Based on the analysis, they reported to correlate the accumulation of anthocyanins with the colour of red and pink fruit pulps, and the expression levels of anthocyanin biosynthesis genes. Fan et al [ 9 ] suggest that their findings “ refute the paradigm of mutual exclusion of anthocyanins and betalains within the same species/tissue ”.…”

Differential Expression Analysis of Genes Related to Flesh Color in <i>Hylocereu polyrhizus</i> and <i>Hylocereu undatus</i>

“…Recent studies have shown that there may be competition between betalanins and anthocyanin metabolic pathway in pitaya. Anthocyanin contributes to the development of pitaya's color partly (Fan et al, 2020).…”