International Journal of Molecular Evolution and Biodiversity, 2025, Vol.15, No.2, 84-98 http://ecoevopublisher.com/index.php/ijmeb 87 Although the current research on drought resistance QTL is still in its infancy, the integration of multi-omics data such as GWAS and transcriptome will significantly improve the efficiency of gene mining. This multidimensional data fusion strategy can not only deeply analyze the genetic basis of drought resistance traits, but also provide new ideas for precision breeding, and promote breakthrough progress in the selection and breeding of drought-resistant rapeseed varieties. 3.4 Epigenetic regulation and gene expression changes under drought stress In a water stress environment, the response of plants to adversity not only depends on the classic transcriptional regulation pathway, but also relies deeply on the participation of epigenetic mechanisms. Such as DNA methylation, histone post-translational modification and the intervention of non-coding RNA, can regulate the expression state of stress resistance genes by regulating chromatin conformation and transcription factor accessibility. These mechanisms together build a dynamic and plastic regulatory network, enabling plants to respond quickly and maintain homeostasis under drought conditions, thereby improving their overall drought tolerance. For example, the BnaC09.Histone gene identified in drought-related GWAS studies has attracted attention because of its close relationship with histone modification (Shahzad et al., 2021). Such modifications may regulate the open state of chromatin, thereby affecting the expression efficiency of downstream stress-resistant genes. WRKY and NAC family transcription factors constitute the core hub of the plant drought resistance regulatory network. Studies have shown that WRKY57 activates downstream target gene expression under drought conditions by specifically recognizing the cis-acting elements of ABA-responsive genes (Jiang et al., 2012). This transcriptional regulation works synergistically with epigenetic mechanisms such as DNA methylation and histone modification, giving plants transcriptional plasticity to cope with environmental stress. This multi-level regulatory network not only enhances the accuracy of gene expression, but also improves the dynamic response ability of plants to adapt to water stress, providing important molecular targets for drought resistance breeding. 4 Molecular and Physiological Mechanisms 4.1 Water-use efficiency and root architecture adaptations Water use efficiency (WUE), as a key indicator for measuring crop drought resistance, directly determines the survival ability and yield performance of rapeseed under drought conditions. With the increasing scarcity of global water resources, improving WUE has become an important direction for modern drought-resistant breeding. To achieve this goal, it is necessary to work together from two dimensions: genetic improvement and physiological regulation: on the one hand, optimize the genetic basis of water use-related traits through molecular breeding methods; on the other hand, use physiological regulation strategies to enhance the plant's resource conversion ability, thereby cultivating new drought-resistant varieties with efficient water use characteristics. Among many physiological traits, the structure and distribution pattern of the root system have a direct impact on water acquisition. Some rapeseed genotypes show a deeper or more rationally distributed root system, which can more effectively absorb water from deep soil and enhance adaptability in drought environments (Araus et al., 2002; Ruggiero et al., 2017). In addition to the root system, controlling stomatal conductance to reduce transpiration rate can also reduce water loss while maintaining photosynthesis efficiency. Simultaneously improving leaf photosynthetic capacity helps maintain high physiological activity under drought stress (Ruggiero et al., 2017; Lin et al., 2020). Whether the root system is developed or not also directly affects the ability to absorb water and nutrients, and is an important physiological indicator for measuring drought resistance. With the continuous advancement of root phenotyping technology, it has become possible to accurately quantify the root structure. Studies have shown that in the increasingly frequent extreme climate events, the resource acquisition ability of the root system is of decisive significance for the stable yield of rapeseed (Wu et al., 2018). Therefore, incorporating root traits into the breeding evaluation system is expected to accelerate the screening and breeding process of drought-resistant varieties.
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