Tree Genetics and Molecular Breeding 2025, Vol.15, No.3, 108-116 http://genbreedpublisher.com/index.php/tgmb 114 9.3 Synthetic biology approaches for customized Citrus aroma profiles In addition to gene editing, synthetic biology is also bringing about new ideas. By integrating transcriptomic and metabolomic data, researchers can identify which genes and enzymes are most important for aroma synthesis, and then recombine them to make aroma components synthesized faster or more (Maoz et al., 2022). For instance, terpene synthases like Cstps1 are one of the key targets. The regulation or engineered expression of these genes can be used for metabolic engineering and aroma optimization (Sharon-Asa et al., 2003; Aragüez and Fernández, 2013). In the future, synthetic biology may enable modular design of Citrus aromas, that is, different aromas can be “customized” to meet different market demands (Conti et al., 2021). 10 Concluding Remarks By analyzing transcriptome and metabolome data together, researchers have identified the main gene regulatory mechanisms behind the formation of Citrus aroma. The aroma of Citrus fruits mostly comes from volatile organic compounds (VOCs) such as terpenoids, which are synthesized through metabolic pathways including terpenoids, phenylalanine and fatty acids. Among them, enzyme-coding genes like Cstps1 and transcription factors such as MYC5 play a very important role in the synthesis of aroma substances and the formation of oil glands. Cstps1 is expressed more strongly after the fruit ripens and is affected by ethylene signaling, which directly influences the accumulation of aroma components like valencene. In addition, a regulatory pathway composed of LMI1, DRNL and MYC5 has also been confirmed to be involved in the development process of oil glands, which helps to enrich aroma substances in specific tissues. Although many important genes and regulatory factors related to aroma have been identified, the genetic mechanism of Citrus aroma remains very complex. There are many types of terpene synthases, and sometimes they have similar functions. Coupled with the fact that the expression of genes varies at different times or sites, this makes functional verification more difficult. In addition, climate, cultivation methods, and the interaction between genes and the environment can also affect the stability of aroma. The aroma performance of different varieties may vary greatly under different conditions. It is still a considerable challenge to achieve precise control and stable inheritance of aroma characteristics. Future research can combine high-throughput omics technologies and gene editing tools to gain a deeper understanding of the networks and regulatory patterns of aroma synthesis. CRISPR can be used to precisely regulate key genes like Cstps1 and MYC5, making the aroma more controllable. It is also necessary to continue studying which transcription factors, regulatory elements or epigenetic mechanisms affect aroma. In the future, if a platform can be built that combines multiple omics data and is equipped with the ability to accurately measure aroma, it will be possible to improve the quality of aroma more quickly and accurately, and cultivate new Citrus varieties with better fragrance and greater popularity. Acknowledgments The author thanks Professor Jian for his modification suggestions and also thanks the group members for helping to organize the research data. Conflict of Interest Disclosure The author affirms that this research was conducted without any commercial or financial relationships that could be construed as a potential conflict of interest. References Alquézar B., Rodríguez A., De La Peña M., and Peña L., 2017, Genomic analysis of terpene synthase family and functional characterization of seven sesquiterpene synthases from Citrus sinensis, Frontiers in Plant Science, 8: 1481. https://doi.org/10.3389/fpls.2017.01481 Aragüez I., and Fernández V., 2013, Metabolic engineering of aroma components in fruits, Biotechnology Journal, 8(10): 1144-1158. https://doi.org/10.1002/biot.201300113 Baccati C., Gibernau M., Paoli M., Ollitrault P., Tomi F., and Luro F., 2021, Chemical variability of peel and leaf essential oils in the Citrus subgenus Papeda (Swingle) and few relatives, Plants, 10(6): 1117. https://doi.org/10.3390/plants10061117
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