Plant Gene and Trait 2024, Vol.15, No.5, 243-252 http://genbreedpublisher.com/index.php/pgt 247 5.2 Impact and challenges The development of transgenic Eucommia ulmoides has significant implications for the rubber industry. The enhanced production of trans-polyisoprene provides a sustainable and economically viable alternative to traditional rubber sources. The genetic insights gained from these studies also pave the way for further improvements in rubber yield and quality. Moreover, the successful application of genetic engineering techniques in Eucommia ulmoides serves as a model for similar efforts in other economically important plant species (Jin et al., 2020). One of the primary challenges in developing transgenic Eucommia ulmoides was the low yield of rubber in natural conditions. To address this, researchers focused on the molecular regulation of key biosynthetic genes. For instance, the promoter activity of the small rubber particle protein (SRPP) gene was analyzed, revealing that its expression is regulated by endogenous hormones and environmental stressors such as drought (Zhao et al., 2023). This understanding allowed for the optimization of gene expression under various conditions, thereby enhancing rubber yield. Additionally, heterologous co-expression of the key rubber biosynthetic genes EuTPT5 and EuREF1 in Nicotiana benthamiana did not result in a significant increase in rubber yield and molecular weight as expected. The biosynthesis of natural rubber is likely a complex process involving multiple enzymes. Therefore, further exploration of rubber biosynthesis may need to be conducted within Eucommia ulmoides itself. 6 Challenges in Developing Transgenic Eucommia ulmoides 6.1 Difficulties in gene transformation and regeneration of transgenic plants Developing transgenic Eucommia ulmoides presents significant technical challenges, particularly in the areas of gene transformation and plant regeneration. The complexity of the E. ulmoides genome, as highlighted by the high-quality de novo assembly, underscores the difficulty in achieving efficient gene transformation and stable integration of transgenes (Li et al., 2020). Additionally, the intricate process of regenerating transgenic plants from transformed cells is compounded by the species-specific requirements for tissue culture and regeneration protocols, which are not yet fully optimized for E. ulmoides (Li et al., 2014; Jin et al., 2020). 6.2 Issues related to the stability of transgenes across generations Ensuring the genetic stability of transgenes across multiple generations is another critical challenge. The stability of transgenes can be influenced by various factors, including the genomic context of the insertion site and the potential for gene silencing. Studies on the genetic linkage map and QTL analysis for E. ulmoides have revealed significant genetic variability and complex inheritance patterns, which could affect the stable expression of transgenes (Jin et al., 2020; Liu et al., 2022). Moreover, the presence of mutation hotspots and heterogeneous sequence divergence in the chloroplast genome further complicates the maintenance of genetic stability in transgenic lines. 6.3 Challenges posed by regulatory frameworks and environmental impact assessments The development and deployment of transgenic E. ulmoides are subject to stringent regulatory frameworks and environmental impact assessments. Regulatory bodies require comprehensive data on the safety and environmental impact of transgenic plants, including potential effects on non-target organisms and gene flow to wild relatives. The unique ecological and economic importance of E. ulmoides, as well as its status as a Tertiary relic plant endemic to China, necessitates thorough environmental assessments to ensure that transgenic varieties do not adversely affect biodiversity or ecosystem stability (Wang et al., 2018; Deng et al., 2022). Additionally, the regulatory approval process can be lengthy and resource-intensive, posing a significant barrier to the commercialization of transgenic E. ulmoides (Chen et al., 2022a; Chen et al., 2022b). 7 Field Trials and Commercialization Prospects 7.1 Field trial results Field trials are essential for evaluating the performance and environmental impact of transgenic Eucommia ulmoides. Recent studies have shown that the phenotypic traits of E. ulmoides can be significantly influenced by both genotype and environmental factors. For instance, a study involving nine clones across six different sites demonstrated that site effects accounted for a larger proportion of variance in most traits, followed by genotype
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