International Journal of Horticulture, 2024, Vol.14, No.5, 297-309 http://hortherbpublisher.com/index.php/ijh 304 patterns of these genes and to investigate how they are regulated under different environmental conditions. Furthermore, the use of chemometric tools in conjunction with molecular biology techniques can optimize the extraction and analysis of betacyanins. For instance, the Box–Behnken Design (BBD) and response surface methodology (RSM) have been successfully applied to evaluate and optimize variables affecting the ultrasound-assisted extraction of betacyanins from red dragon fruit, ensuring accurate determination of these pigments (Carrera et al., 2021). 7 Case Studies 7.1 Betalain synthesis in red-fleshed dragon fruit Betalain pigments, including betacyanins and betaxanthins, are the primary pigments responsible for the red color of red-fleshed dragon fruit. The synthesis of betalains in dragon fruit involves multiple key genes. Zhou et al. (2020) found that the formation of red flesh is mainly due to the upregulation of the key gene CYP76ADs in the betacyanin pathway, which is regulated by the WRKY44 transcription factor. Using transcriptome (RNA-Seq) and metabolome (UPLC-MS/MS) analysis, the study conducted an in-depth investigation of three different-colored dragon fruit types. The results showed that the formation of red flesh largely depends on the increased tyrosine content, which further drives the downstream steps of the betacyanin pathway (Figure 3). Figure 3 Betalain biosynthesis pathway (and tyrosine biosynthesis from arogenate) (Adopted from Zhou et al., 2020) Image caption: The figure illustrates the gene regulatory network of the betalain synthesis pathway in pitaya, covering the steps from tyrosine to the formation of red pigments. The different colored boxes represent the peel and pulp colors of different types of pitaya (red, green, yellow). The figure details the differential expression of key enzymes such as CYP76ADs, TYDCs, and DODAs, with arrows indicating the direction of the metabolic pathway. This figure reveals that the upregulation of the CYP76ADs gene is crucial for the formation of red peel and pulp, further supporting the conclusion that red pigment synthesis is primarily regulated by the betalain pathway (Adapted from Zhou et al., 2020)
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