Plant Gene and Trait 2024, Vol.15, No.5, 243-252 http://genbreedpublisher.com/index.php/pgt 246 acquisition of a high-quality haploid chromosome-scale genome assembly for E. ulmoides. This assembly, achieved using PacBio and Hi-C technologies, provides a robust foundation for gene editing by offering detailed insights into the genome structure and evolution, which are crucial for targeted genetic modifications (Li et al., 2020). Additionally, the identification of 26 001 predicted protein-coding genes anchored to the 17 chromosomes facilitates the precise editing of genes involved in rubber biosynthesis and other industrially relevant pathways. 4.2 Transformation methods Transformation methods are essential for introducing new genetic material into E. ulmoides. One widely used method is Agrobacterium-mediated transformation, which has been successfully employed to obtain transgenic lines of Arabidopsis thaliana expressing Eucommia ulmoides genes. For instance, the promoter sequences of the Eucommia ulmoides SRPP (EuSRPP) genes were introduced into Arabidopsis via Agrobacterium, resulting in stable expression in various plant tissues (Zhao et al., 2023). Furthermore, researchers have established a protoplast isolation and transient transformation system for Eucommia ulmoides, laying the foundation for high-throughput analysis of gene function studies in the future (Hu et al., 2024). Simultaneously, there has been some research on the method of using Agrobacterium infection of the hypocotyl of Eucommia ulmoides to induce new plantlets (Ran et al., 2022), this method not only demonstrates the feasibility of genetic transformation in E. ulmoides but also highlights the potential for using similar techniques to enhance the rubber biosynthesis pathway and other desirable traits in this species. 4.3 Promoters and regulatory elements Promoters and regulatory elements play a critical role in the expression of transgenes in E. ulmoides. The activity of these elements can be influenced by various environmental and endogenous factors. For example, the promoter activity of the Eucommia ulmoides SRPP genes was found to be regulated by methyl jasmonate (MeJA), gibberellin (GA3), and drought pathways. The expression activity of these promoters varied under different treatments, indicating that they are responsive to hormonal and stress signals (Zhao et al., 2023). This knowledge is invaluable for designing transgenic constructs with promoters that can drive the expression of target genes in a controlled manner, thereby optimizing the production of industrially important compounds in E. ulmoides. 5 Case Study: Successful Development of Transgenic Eucommia ulmoides for Enhanced Rubber Production 5.1 Methodology and results The development of transgenic Eucommia ulmoides aimed at enhancing rubber production has been a significant focus in recent years. Eucommia ulmoides, known for its production of trans-polyisoprene rubber, presents a valuable alternative to traditional rubber sources. The primary approach involved the overexpression of key genes involved in the rubber biosynthesis pathway. One notable project isolated and overexpressed the isopentenyl diphosphate isomerase (IPI) gene in Eucommia ulmoides. This gene plays a crucial role in the conversion of isopentenyl diphosphate to dimethylallyl diphosphate, a precursor in the biosynthesis of trans-polyisoprene (Chen et al., 2012). The transformation was achieved using Agrobacterium-mediated techniques, which allowed for the stable integration and expression of the transgene in the plant genome. The transgenic lines of Eucommia ulmoides exhibited significant improvements in rubber production. Specifically, the overexpression of the EuIPI gene resulted in a 3- to 4-fold increase in the total content of trans-polyisoprenes compared to non-transgenic controls (Chen et al., 2012). Additionally, transcriptome analysis identified several differentially expressed genes involved in terpenoid biosynthesis, further supporting the enhanced rubber production in transgenic lines (Jin et al., 2020). Li et al. (2020) obtained three authentic Eucommia haploid plants (Figure 1) through flow cytometry and analysis of anatomical sections of stem tips, and performed genome sequencing and assembly. The successful assembly of a high-quality haploid genome also provided insights into the genetic basis of rubber biosynthesis, facilitating further genetic improvements.
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