Tree Genetics and Molecular Breeding 2025, Vol.15, No.3, 128-137 http://genbreedpublisher.com/index.php/tgmb 129 several β-ketoacyl-ACP synthetases (KAS I/II/III), hydroxyacyl-ACP dehydrogenase (HAD) and enoyl-ACP reductase (EAR). These synthesized fatty acids are then activated by long-chain acyl-CoA synthetase (LACS) and then transferred to the endoplasmic reticulum, where they are further modified and finally assembled into TAG. Key synthases also include triglyceride synthase (DGAT) and phosphatidylcholine:diacylglycerol acyltransferase (PDAT) (Figure 1) (Gong et al., 2020; Ye et al., 2020; Yang et al., 2024; Zhu et al., 2024). Figure 1 The regulatory network of key lipid metabolites in Changlin40 (Adopted from Zhu et al., 2024) Image caption: (a) The metabolic pathway for lipid. The red-blue heatmap represents the expression levels of corresponding catalytic genes at different seed kernel developmental stages, while the green-purple heatmap represents the content of corresponding metabolites at different seed kernel developmental stages. PDH, Pyruvate dehydrogenase; ACCase, Acetyl-CoA carboxylase; ACP, Acyl carrier protein; KASIII, Beta-ketoacyl-(acyl-carrier-protein) synthase III; FATB, Fatty acyl-ACP thioesterase B; KASII, Beta-ketoacyl-(acyl-carrier-protein) synthase II; SAD, Stearoyl-ACP desaturase; FATA, Fatty acyl-ACP thioesterase A; LACS, Long-chain Acyl-CoA synthetase; GPAT, Glycerol-3-phosphate acyltransferase; LPAT, Lysophosphatidic acid acyltransferase; PAP, Purple acid phosphatase; DGAT, Diacylglycerol acyltransferase; FAD2, Fatty acid desaturase 2; FAD3, Fatty acid desaturase 3. (b) Schematic of Camellia oil biosynthesis in Changlin40 seed kernel (Adopted from Zhu et al., 2024) 2.2 Key genes and enzymes involved in triacylglycerol formation Throughout the entire process of oil synthesis, many key genes and enzymes play significant roles. Through the joint study of transcriptome and proteome, it was found that in the later stage of seed maturation, the expressions of genes such as ACCase, KAS family, SAD, FAD2/3, LPAAT, DGAT and PDAT were all very high. All of these contribute to the massive accumulation of oils and fats (Ye et al., 2020; Yang et al., 2024). In addition, studies have also found that WRI1 transcription factors can interact with 17 enzymes related to lipid synthesis, and transcription factors such as MYB and ZIP also play a role in the regulatory process (Gong et al., 2020; Li et al., 2022). Population genome studies have pointed out that genes such as SAD and KAS III were selected by humans to have better alleles during the domestication process of Camellia oleifera, which helps to increase the yield and quality of oil (Lin et al., 2022; Zhu et al., 2024). 2.3 Tissue-specific and developmental regulation of oil content The accumulation of oil is also related to the stage of seed development and different tissue parts. When seeds enter the mature stage, the oil content increases rapidly, and at this time, the expression of some key synthetic genes also rises simultaneously (Zhang et al., 2021; Yang et al., 2024). The expression levels of genes such as SAD and FAD2 vary among different varieties and different parts, which leads to differences in lipid composition and content (Lin et al., 2018; Zhu et al., 2024). Furthermore, transcription factors such as MYB are specifically expressed at different developmental stages of seeds, and they can regulate lipid metabolism and the maturation process of seeds (Li et al., 2022). Through multiple omics studies, it has also been found that the expression of these genes and proteins is finely regulated by developmental stage and tissue type (Ye et al., 2020; Ye et al., 2021).
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