International Journal of Molecular Evolution and Biodiversity, 2025, Vol.15, No.2, 111-123 http://ecoevopublisher.com/index.php/ijmeb 118 8.2 Transcriptional regulatory features of drought response In the face of drought stress, the Brassica napus genome initiates a complex response program. The expression of 1845 genes changed significantly, forming a typical "early response-continuous adaptation" regulation pattern (Fang et al., 2022). The BnaA01.CIPK6 gene is like a molecular commander, and its overexpression increased the plant survival rate by 65%. DELLA proteins form a dynamic complex with ABA signaling components and play a key role in stomatal regulation (Wu et al., 2020). The expression adjustment of photosynthesis-related genes is particularly exquisite: the expression of Calvin cycle enzyme encoding genes such as FBPase and PRK is downregulated, while the photorespiration pathway genes are upregulated by 2-3 times (Taghvimi et al., 2024). 8.3 Molecular breeding strategies for drought resistance improvement Modern breeding technology is breaking through traditional limitations. LEA3 gene transformation strains show amazing characteristics: photosynthetic efficiency is increased by 32% and ROS accumulation is reduced by 45% (Liang et al., 2019). Precise manipulation of the ABA signaling pathway has opened up a new path. By regulating the stability of DELLA proteins, spatiotemporal regulation of stomatal opening and closing can be achieved (Wu et al., 2020). The discovery of lncRNA brought unexpected surprises, and some non-coding transcripts showed a high correlation of 0.82 with drought resistance (Tan et al., 2020). These breakthroughs provide a diversified technical route for designing drought-resistant varieties. 9 Application of Genetic Engineering and Synthetic Biology in the Improvement of Brassica napus 9.1 Precision gene editing of CRISPR-Cas9 system As an important tool in modern molecular breeding, CRISPR-Cas9 system has shown strong advantages in the precise transformation of rapeseed genome. Studies have found that knocking out the BnaA9.WRKY47 gene can increase the expression of boron transporter gene by about 2.5 times, significantly improving the growth performance of plants in a boron-deficient environment (Feng et al., 2019). There are also major breakthroughs in disease resistance improvement: by co-editing two WRKY family genes, the infection rate of sclerotinia disease was reduced from the initial 75% to only 25% (Sun et al., 2018). In addition, the male sterility system based on gene editing is gradually becoming an important means of hybrid breeding. After editing BnaRFL11, pollen vitality dropped sharply by 98%, greatly improving the breeding efficiency of hybrid lines (Farooq et al., 2022). At the same time, the establishment of the hairy root transformation system also provides an efficient platform for functional gene verification, shortening the experimental cycle by 3-5 times, significantly improving the speed and repeatability of functional research (Jedličková et al., 2022). 9.2 Development and application of synthetic biology elements The rapid development of synthetic biology is opening up a new direction for crop genetic improvement. Taking WRKY47 as an example, after engineering design, its transcription factor can simultaneously sense boron deficiency and drought signals, forming a dual stress response module (Feng et al., 2019). This modular construction method is expected to significantly enhance the adaptability of crops to complex adversities. Genome association analysis further revealed that regulatory SNPs at transcription factor binding sites are important factors affecting oil content, and their explanation of natural phenotypic variation can reach 18% (Klees et al., 2021). Relying on this type of molecular information, researchers have designed a series of highly efficient synthetic promoters, whose transcriptional activation ability is 40% to 60% higher than that of natural promoters, providing a more flexible and reliable tool set for the precise regulation of target traits. 9.3 Technology application prospects and existing challenges Although gene editing technology has great potential, it still faces many difficulties in practical applications. Off-target effects have always been a hidden concern that limits its widespread application, but with the introduction of high-fidelity Cas9 variants, its non-specific cutting probability has been controlled below 0.1%, significantly improving editing accuracy.
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