Bioscience Evidence 2024, Vol.14, No.5, 206-217 http://bioscipublisher.com/index.php/be 207 2 Biochemical Pathways of α-Linolenic Acid Biosynthesis 2.1 Key enzymes involved in ALA biosynthesis Desaturases are crucial enzymes in the biosynthesis of α-linolenic acid (ALA). These enzymes introduce double bonds into fatty acid chains, a key step in the formation of polyunsaturated fatty acids like ALA. In Eucommia ulmoides, the high expression of the ω-3 fatty acid desaturase coding gene EU0103017 has been identified as a significant factor contributing to the high ALA content in the plant. This enzyme catalyzes the conversion of linoleic acid (LA) to ALA by introducing a double bond at the ω-3 position, which is essential for the biosynthesis of ALA. Elongases are another group of enzymes that play a pivotal role in fatty acid metabolism by extending the carbon chain length of fatty acids. Although the specific elongases involved in ALA biosynthesis in Eucommia ulmoides have not been explicitly detailed, studies in mammalian systems have shown that elongases such as Elovl3, Elovl4, Elovl5, and Elovl6 are integral to the elongation process (Du et al., 2023). These enzymes add two-carbon units to the fatty acid chain, which is a critical step preceding the desaturation process that ultimately leads to the formation of ALA. 2.2 Gene regulation in the ALA biosynthetic pathway Transcription factors are proteins that regulate the expression of genes involved in various biosynthetic pathways, including those for ALA. In Eucommia ulmoides, specific transcription factors that influence the expression of desaturase and elongase genes have not been fully characterized. However, the regulation of these enzymes is likely controlled by a complex network of transcription factors that respond to developmental and environmental cues, ensuring the proper synthesis of ALA. Epigenetic modifications, such as DNA methylation and histone modification, play a significant role in the regulation of gene expression. These modifications can influence the activity of genes involved in the ALA biosynthetic pathway by altering chromatin structure and accessibility. While specific epigenetic modifications in Eucommia ulmoides have not been extensively studied, it is plausible that such mechanisms are involved in the regulation of key enzymes like desaturases and elongases, thereby affecting ALA biosynthesis (Gregory et al., 2011). 2.3 Comparative analysis of ALA biosynthesis inEucommia ulmoides and other plants The biosynthetic pathway of ALA in Eucommia ulmoides shares several similarities with other plants. In general, the process involves the desaturation of linoleic acid to produce ALA, a reaction catalyzed by ω-3 fatty acid desaturases. This pathway is conserved across many plant species, indicating a common evolutionary origin for the enzymes involved in ALA biosynthesis. One unique aspect of ALA biosynthesis in Eucommia ulmoides is the exceptionally high expression of the ω-3 fatty acid desaturase coding gene EU0103017, which significantly contributes to the high ALA content inEucommia ulmoides (Wang et al., 2022). This high expression level may be a result of specific regulatory mechanisms or evolutionary adaptations that enhance the plant's ability to produce ALA, distinguishing it from other species with lower ALA content. By understanding these biochemical pathways and regulatory mechanisms, researchers can better appreciate the unique aspects of ALA biosynthesis in Eucommia ulmoides and potentially apply this knowledge to improve ALA production in other plants (Lei et al., 2017). 3 Genetic Basis of α-Linolenic Acid Biosynthesis 3.1 Identification and characterization of ALA-related genes inEucommia ulmoides High-throughput sequencing has been instrumental in identifying genes involved in the biosynthesis of α-linolenic acid (ALA) in Eucommia ulmoides. Transcriptome sequencing of E. ulmoides seeds at different developmental stages has revealed numerous unigenes associated with fatty acid biosynthesis. For instance, among the 23 314 unigenes identified in the transcriptome of male and female flowers of E. ulmoides during the flowering period, 56 were related to fatty acid synthesis, including key enzymes such as 3-ketoacyl-ACP reductase and β-ketoacyl-ACP synthase II (Zhao et al. 2015). Another study utilized RNA-sequencing to identify genes related to glycolytic metabolism, which is crucial for providing intermediates for ALA biosynthesis (Feng et al., 2016). Functional annotation of the identified genes has provided insights into their roles in ALA biosynthesis. For example, genes encoding ω-3 fatty acid desaturase (FAD) enzymes, such as FAD2 and FAD3, have been
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