Tree Genetics and Molecular Breeding 2025, Vol.15, No.3, 98-107 http://genbreedpublisher.com/index.php/tgmb 103 synthesis (Shi et al., 2021). These findings also indicate that the regulatory process of anthocyanins is actually quite complex. It is not a single gene acting alone, but rather multiple proteins working together. 7 Genetic and Epigenetic Regulation of Anthocyanin 7.1 Promoter elements and cis-regulatory motifs There are many cis-regulatory elements in the promoters of genes related to anthocyanin synthesis. These small fragments can sense light, hormones and developmental signals, thereby regulating whether genes are functioning or not. Transcription factors such as R2R3-MYB recognize these elements. Some can activate genes, and some can inhibit them, thus affecting the amount of anthocyanins (Zhao et al., 2023). Moreover, the natural differences in the promoter regions of different varieties can also cause variations in anthocyanin content (Yang et al., 2022). 7.2 DNA methylation and histone modification DNA methylation and histone modification are another set of regulatory mechanisms, which belong to epigenetic regulation. Studies have found that if the methylation level in the promoter region is high, the related genes are prone to suppression and anthocyanins are less (Sun et al., 2023). For instance, in chrysanthemums, if the methylation of the promoter of the CmMYB6 gene is high, the flower color will be light. But if methylation is removed, anthocyanins will come back (Tang et al., 2022). In addition, some modifications on histones can also regulate expression. H3K4me3 can promote gene expression, while H2A.Z has the opposite effect, and the two balance each other (Cai et al., 2018). Histone demethylases (such as JMJ25, IBM1) also regulate the activity of anthocyanin genes by eliminating certain modifications (such as H3K9me2) (Fan et al., 2018; Zheng et al., 2019; Fan et al., 2024). 7.3 Small RNAs and post-transcriptional regulation Small RNAs (such as miRNA and siRNA) are also involved in regulation. These small molecules can directly bind to the mRNA of anthocyanin synthesis-related genes, causing them to degrade or be untranslated (Zhao et al., 2023). Some can also affect transcription factors, thereby indirectly regulating the entire anthocyanin synthesis pathway (Khan and Abbas, 2023). These mechanisms work together to ensure that plants can flexibly control the synthesis of anthocyanins according to different developmental stages or environmental changes. 8 Case Study: Functional Analysis of MrMYB1 in Regulating Anthocyanin Accumulation 8.1 Background and research hypothesis The fruit color of Morella rubra is very rich, ranging from white, red to deep purple-red. This color difference is mainly caused by the varying content of anthocyanins. The synthesis process of anthocyanins is controlled by multiple genes, among which MYB transcription factors play a very important role. Studies have found that MrMYB1 is a key R2R3-MYB transcription factor in bayberry, and its expression level is highly correlated with the amount of anthocyanins in the fruit (Niu et al., 2010). So it is speculated that MrMYB1 might affect the color of Morella rubra by regulating the expression of genes related to anthocyanin synthesis. 8.2 Experimental design and key findings Researchers first examined the expression of MrMYB1 in different colored varieties of Morella rubra and found that the higher the expression of this gene, the more anthocyanins there were in the fruits. When they wrapped the fruits in fruit bags, the expression of MrMYB1 and other anthocyanin synthesis genes decreased, and the anthocyanin content also decreased accordingly. Then, they overexpressed MrMYB1 in tobacco, resulting in a significant increase in anthocyanins. They also found that the promoters of some key enzymes were activated. In addition, meaningless mutant versions of MrMYB1 were also found in the white and red varieties. This mutation may render this gene “ineffective”, resulting in a lighter fruit color (Niu et al., 2010). Subsequent experiments also indicated that MrMYB1 could interact with MrbHLH1 and MrWD40-1 to form a complex, and this combination could significantly promote the synthesis of anthocyanins (Liu et al., 2013a; Liu et al., 2013b). 8.3 Implications for fruit color improvement in bayberry breeding MrMYB1 is an important gene that regulates the synthesis of anthocyanins in Morella rubra. The level of its expression will directly affect the color of the fruit. In the future, if MrMYB1 and its partner genes can be regulated through molecular breeding, it will be possible to cultivate new varieties of Morella rubra with brighter
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