Molecular Plant Breeding 2024, Vol.15, No.6, 391-402 http://genbreedpublisher.com/index.php/mpb 395 Moreover, genes involved in the biosynthesis of valuable metabolites, such as those encoding enzymes in the terpenoid and flavonoid pathways, can be targeted to increase the production of these compounds. By leveraging the precision of CRISPR-Cas9 and other gene editing tools, it is possible to introduce specific mutations or insertions that enhance the expression or activity of these key genes, thereby improving the overall productivity and quality of Eucommia ulmoides (Park et al., 2022; Guo et al., 2023) 3.3 De novo genome assembly contributions The application of de novo genome assembly techniques has greatly advanced the development of genetic improvement technologies for Eucommia ulmoides. High-quality genome assemblies provide a comprehensive reference for identifying target genes and their regulatory networks. In recent years, research has shifted towards generating detailed genomic maps of Eucommia ulmoides, including annotations of genes, regulatory elements, and structural variations. These genomic resources are invaluable for designing precise gene editing strategies. For example, the identification of conserved sequences and regulatory motifs can guide the selection of target sites for CRISPR-Cas9 editing. Additionally, genome assemblies facilitate the study of gene function and interaction, enabling researchers to predict the outcomes of genetic modifications more accurately. The integration of genomic data with gene editing technologies holds great promise for optimizing the genetic improvement of Eucommia ulmoides (Han et al., 2020; Li et al., 2020a; Sharma et al., 2020). In conclusion, the application of advanced gene-editing tools such as CRISPR-Cas9, combined with the identification of key target genes and the integration of genomic data, offers immense potential for improving the yield and quality of Eucommia ulmoides. Continued research and development in these areas will pave the way for more efficient and precise genetic improvements, ultimately benefiting the cultivation and utilization of this valuable plant species. 4 Enhancing Productivity through Genetic Modification 4.1 Improving growth rates: strategies for modifying genes related to faster growth The improvement of Eucommia ulmoides growth rate through genetic modification techniques involves the targeted regulation of specific genes responsible for plant development and growth. One promising approach is the overexpression of aquaporin genes such as EuPIP1;1. Studies have shown that constitutive overexpression of EuPIP1;1 in Arabidopsis thaliana promotes leaf growth, accelerates bolting and flowering, and up-regulates genes related to growth and flowering, such as AtPIF4 and AtTCP14 (Chen et al., 2022a). Additionally, gene pyramiding, which involves the simultaneous introduction of multiple beneficial genes, has been demonstrated to significantly enhance plant growth. For instance, the combined overexpression of AVP1, OsSIZ1, and Fld in creeping bentgrass resulted in superior growth performance under both normal and stress conditions (Zhao et al., 2023a). 4.2 Enhancing stress resistance: genetic pathways to enhance drought, pest, and disease resistance Enhancing the stress resistance of Eucommia ulmoides can be achieved by modifying genetic pathways that confer tolerance to drought, pests, and diseases. The overexpression of aquaporin genes such as EuPIP1;1 and EuPIP1;2 has been shown to improve drought and salt stress tolerance in transgenic plants. These genes help maintain ion homeostasis, reduce membrane damage, and improve osmotic adjustment under stress conditions (Figure 2) (Chen et al., 2022a; 2022b). Additionally, the NAC transcription factor family plays a crucial role in plant adaptation to environmental challenges. The identification and characterization of 69 NAC genes in Eucommia ulmoides suggest that these genes can be targeted to enhance drought stress tolerance (Wang et al., 2023b). Furthermore, the use of plant growth-promoting rhizobacteria (PGPR) can activate plant adaptive defense systems, improving drought tolerance and overall growth (Gowtham et al., 2022). 4.3 Increasing metabolite production: genetic modifications to improve production of valuable compounds such as gutta-percha Increasing the production of valuable compounds like gutta-percha in Eucommia ulmoides can be achieved
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