Rice Genomics and Genetics 2024, Vol.15, No.6, 265-276 http://cropscipublisher.com/index.php/rgg 267 A comprehensive understanding of the characteristics, classification, phylogenetic relationships, and expression patterns of R2R3-MYB genes enables researchers to gain valuable insights into the regulatory mechanisms underlying anthocyanin biosynthesis and plant adaptation in dark purple rice. Figure 1 Expression analysis of anthocyanin biosynthesis pathway genes in black and white rice panicles at various developmental stages (Adopted from Upadhyaya et al., 2021). Image caption: (A) Generalized anthocyanin biosynthesis scheme in plants. Genes encoding enzymes are indicated in uppercase letters: CHS, chalcone synthase; CHI, chalcone isomerase; F3H, flavanone 3-hydroxylase; F3’H, flavanone 3’-hydroxylase; DFR, Dihydroflavonol 4-reductase; ANS, Anthocyanidin synthase; GT, UDP-glucose:flavonoid-3-O-glycosyltransferase. Structural and regulatory genes have been labeled in the scheme for clarity. (B-H) qRT-PCR expression analysis in panicle tissue of black and white rice for anthocyanin biosynthesis genes CHS (B), CHI (C), F3H(D), F3’H(E), DFR(F), ANS (G), and C1 (H). The developmental stages are 0, 3, 6, 9, 12, and 15 DAP, where DAP represents days after pollination. ACTIN was used as an internal control. Data are represented as relative expression level in black rice panicle with respect to white rice at corresponding stages and genes. Data are depicted as mean±SD of three independent experiments (n=3 biological replicates, each containing six plants); *P<0.01, **P<0.001, and ***P<0.0001 show statistically significant differences with control that is, white rice panicle using one-way ANOVA followed by Dunnett's test. (I) Heatmap showing the expression level of each gene in both rice varieties at variable seed developmental stages. The expression profile of enzymes was represented in terms of relative expression as compared to 0 DAP, obtained from qRT-PCR experiment. The upper panel shows different color phenotypes of pericarp tissue at successive developmental stages of grain filling (Adopted from Upadhyaya et al., 2021) 3 Environmental Factors Affecting Anthocyanin Biosynthesis 3.1 Light intensity and quality The influence of light on anthocyanin biosynthesis is a critical factor in environmental studies (Song et al., 2022). It has been demonstrated that light intensity and quality can markedly upregulate the expression of R2R3-MYB TFs, which are pivotal regulators of anthocyanin biosynthesis (Ma et al., 2021). For example, the expression of TaPL1 in wheat coleoptiles is markedly enhanced by light, resulting in elevated anthocyanin accumulation (Shin
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