Tree Genetics and Molecular Breeding 2025, Vol.15, No.3, 98-107 http://genbreedpublisher.com/index.php/tgmb 99 Although the overall differences are not significant, female and male strains can be clearly distinguished by some specific gender markers (such as ZJU062 and ZJU130). Zhejiang is the region with the richest genetic diversity of Morella rubra. Varieties such as ‘Biqi’, ‘Dongkui’ and ‘Pink’ are derived from different genetic resources (Jia et al., 2015). Now, the genome, transcriptome and germplasm resources of bayberry have been sorted out and a database has been established, laying a good foundation for breeding research (Ren et al., 2021). 2.2 Geographic distribution and ecological adaptability Morella rubra are mainly distributed in the tropical and subtropical regions of our country. Due to its suitable climate, Guangdong Province is a place where a large number of Morella rubra are grown. Different varieties are distributed in 41 counties. There are also many wild Morella rubra in Guangxi, and these wild populations have a high degree of genetic diversity. Their distribution is closely related to the local climate and environment. According to the color and luster of the peel, Morella rubra can roughly be divided into three types: black, red and white. Varieties of different colors also have their own characteristics and are suitable for promotion and cultivation. From the perspective of population genetics, the reason why Morella rubra can be widely cultivated in China is their strong ability to adapt to the environment. Meanwhile, gene drift and limited gene flow also have an impact on its genetic structure. 2.3 Fruit development and pigmentation traits The flesh development process of Morella rubra is a rather complex one, which is regulated by many hormones and genes. Plant hormones such as auxin (IAA), jasmonic acid (JA), abscisic acid (ABA), and gibberellin change levels at different stages of fruit development. Especially the interaction among IAA, JA and ABA plays a particularly significant role during critical periods. The study also found that some genes, such as LAX2, LAX3 (responsible for auxin transport), JAZ6 (regulating JA signaling), KAN1 and KAN4 (involved in multiple hormone signaling), are closely related to pulp development. Immunofluorescence experiments also revealed that auxin was mainly concentrated in the vascular bundles and outer cells in the middle of the pulp. This uneven distribution might affect the shape of the pulp (Figure 1) (Fu et al., 2025). In addition, the fruit color of Morella rubra is classified into three types: black, red and white. The differences in color and luster are due to the variations in the accumulation of pigments such as anthocyanins. 3 Anthocyanin Biosynthesis Pathway 3.1 Phenylpropanoid and flavonoid pathways The synthesis process of anthocyanins is part of two pathways: phenylpropane metabolism and flavonoid synthesis. This process starts with phenylalanine and, through the action of some enzymes, will generate the precursors of flavonoids. Then, plants convert these precursor substances into various flavonoids through the flavonoid synthesis pathway, among which anthocyanins are included (Pratyusha and Sarada, 2022; Dutt et al., 2023). This path not only determines the color of the plants but is also related to their stress resistance, growth and development, and other functions. 3.2 Key enzymes: CHS, CHI, F3H, DFR, ANS, UFGT During the synthesis of anthocyanins, some structural genes play significant roles, such as CHS, CHI, F3H, DFR, ANS, and UFGT. These enzymes will transform substances one by one and finally synthesize different types of anthocyanins (Raziq et al., 2024; Zhu et al., 2025). Research has found that the expression levels of these genes can affect the content of anthocyanins, and their expressions also vary at different developmental stages or in different organs. For instance, when the fruit begins to change color, the expression of these genes will significantly increase, which is conducive to the synthesis and accumulation of anthocyanins (Dutt et al., 2023; Sun et al., 2025). 3.3 Regulatory genes: MYB, bHLH, and WD40 transcription factors In addition to structural genes, the synthesis of anthocyanins is also controlled by some regulatory proteins, mainly three types of transcription factors: MYB, bHLH and WD40. These proteins can together form a regulatory group called the MBW complex, which can directly control the expression of structural genes and is the core of the entire regulatory network (Chen et al., 2019; Jiang et al., 2023). Among them, the factors of the
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