Genomics and Applied Biology 2024, Vol.15, No.6, 276-284 http://bioscipublisher.com/index.php/gab 279 qA07.SOC, being consistently detected across multiple environments (Zhao et al., 2022). Similarly, in Camelina sativa, QTL mapping identified loci associated with oil content and fatty acid composition, aiding in the breeding of high-yielding varieties (Li et al., 2021). These studies suggest that similar QTL mapping efforts in Camellia could reveal critical loci for oil content improvement. 4.3 Identification of genetic markers linked to high oil content traits The identification of genetic markers linked to high oil content traits is crucial for the genetic improvement of Camellia species. In Camellia oleifera, SNP markers within genes coding for fatty acid desaturases have been linked to oil content and quality. Specifically, six SNP markers from the genes Cofad2-A, CoSAD1, and CoSAD2 were validated and found to be significantly associated with oil content traits (Lin et al., 2019). Additionally, transcriptomic analyses have identified differentially expressed genes (DEGs) involved in lipid metabolism and oil biosynthesis, providing further candidate markers for breeding programs (Lin et al., 2018; Gong et al., 2020). These genetic markers and DEGs offer valuable tools for marker-assisted selection and the development of Camellia varieties with enhanced oil content. 5 Candidate Genes for Oil Quality and Quantity 5.1 Identification of specific genes associated with oil composition The identification of specific genes associated with oil composition in Camellia species has been a focal point of recent research. In Camellia oleifera, key genes such as CoSADandCofad2, which code for fatty acid desaturases, have been linked to oil content and fatty acid composition. These genes were found to contain significant single nucleotide polymorphisms (SNPs) and insertion-deletion (InDel) variations that correlate with oil traits, explaining a substantial proportion of phenotypic variance (Lin et al., 2019). Additionally, transcriptomic analyses have identified differentially expressed genes (DEGs) involved in lipid metabolism, such as stearoyl-ACP desaturases (SADs) and fatty acid desaturase 2 (FAD2), which play crucial roles in the biosynthesis of oleic acid (Lin et al., 2018; Wu et al., 2019). 5.2 Functional analysis of candidate genes in oil accumulation Functional analysis of candidate genes has provided insights into their roles in oil accumulation. For instance, the coordinated high expression of upstream genes like HAD, EAR, and KASI has been shown to increase the levels of C16:0-ACP, a precursor for oleic acid biosynthesis. Concurrently, the high expression of SAD genes accelerates oleic acid synthesis, while the low expression of downstream genes such as FAD2, FAD3, FAD7, FAD8, and FAE1 reduces the conversion of oleic acid to other fatty acids, ensuring its accumulation (Wu et al., 2019). Proteomic studies have also highlighted the importance of enzymes like diacylglycerol acyltransferase and glyceraldehyde-3-phosphate dehydrogenase in oil biosynthesis, further validating the roles of these candidate genes (Ye et al., 2021; Gong et al., 2022). 5.3 Comparative analysis of gene expression in high vs. low oil-yielding camellia varieties Comparative transcriptomic analyses between high and low oil-yielding Camellia varieties have revealed significant differences in gene expression profiles. High oil-yielding varieties exhibit a coordinated upregulation of genes involved in fatty acid biosynthesis and oil accumulation, such as SAD and WRI1, while low oil-yielding varieties show higher expression of genes involved in fatty acid degradation (Wu et al., 2019; Ye et al., 2020). These studies have identified critical transcription factors, including ABI3, FUS3, LEC1, and WRI1, which regulate the expression of multiple genes associated with oil biosynthesis and accumulation (Wu et al., 2019). Additionally, the expression patterns of lipid biosynthesis genes have been shown to correlate with the stages of seed development, further emphasizing the dynamic regulation of oil content in Camellia species (Lin et al., 2018; Gong et al., 2020). 6 Advances in Genomic Selection and Breeding for Oil Content 6.1 Applications of genomic selection techniques to improve oil yield Genomic selection techniques have significantly advanced the breeding of Camellia species for enhanced oil yield. The identification of single nucleotide polymorphisms (SNPs) and insertion-deletion (InDel) markers associated
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