Molecular Plant Breeding 2025, Vol.16, No.2, 105-118 http://genbreedpublisher.com/index.php/mpb 106 This study is expected to explore the transcriptional regulation and gene network of rice under water deficient conditions, identify key transcription factors (TFs) and genes differentially expressed under drought stress, and comprehensively analyze the genetic diversity and combinatorial ability of different rice genotypes under water deficit conditions, in order to accelerate the breeding of drought-resistant rice varieties to improve rice yield and ensure food security under climate change conditions. 2 Water Deficit Stress in Plants 2.1 Definition and types of water deficit Water deficit, that adversely affects plant growth and productivity. It occurs when the water availability in the soil is insufficient to meet the plant’s needs, they begin to experience drought stress, leading to a range of physiological and biochemical changes. Water deficit can be classified into different types based on its duration and intensity, including transient, moderate, and severe drought conditions. Transient drought，where plants face short-term water shortage, can often be overcome by their own physiological regulatory mechanisms, such as adjusting the opening and closing of stomata to reduce water loss. Moderate drought, with a continuous decrease in soil moisture, results in a significant slowdown in plant growth rate, possible wilting of leaves, reduced photosynthetic efficiency, and limited root expansion, requiring human intervention through irrigation to ensure normal plant growth. Severe drought, where the soil loses almost all its moisture, leaves plants unable to obtain sufficient water through natural means. This not only leads to stagnate in plant growth but may also cause widespread plant death, having a profound impact on agricultural production and ecosystems. The latter two types of drought have a serious impact on plant development and yield (Volante et al., 2017; Sakran et al., 2022). 2.2 Physiological and biochemical impacts of water deficit on plants Water deficit stress triggers a complex array of physiological and biochemical responses in plants. Physiologically, it leads to reduced leaf water potential, stomatal closure, decreased photosynthetic rate, and impaired growth (Basu et al., 2016; Zhu et al., 2021). Biochemically, plants under water deficit conditions exhibit increased synthesis of ABA, which plays a crucial role in mediating stress responses. ABA induces the expression of genes involved in osmotic adjustment, cellular dehydration tolerance, and protective enzyme production (Baldoni etb al., 2016; Seeve et al., 2017). Additionally, water deficit stress results in the accumulation of reactive oxygen species (ROS), which can cause oxidative damage to cellular components. Plants maintain normal physiological functions by enhancing the activity of antioxidant enzymes, synthesizing other antioxidants (such as ascorbic acid and glutathione), producing osmoprotectants (such as proline and soluble sugars), and synthesizing specific osmoregulatory substances (such as betaines and polyols) (Mittler, 2002; Yun et al., 2010; Kim et al., 2019; Basu and Roychoudhury, 2021). 2.3 Specific challenges and responses in rice Rice, as a crop with high water demand, is highly sensitive to water deficit stress, which poses severe challenges to its growth and productivity. Under water deficit conditions, rice exhibits significant reductions in traits such as plant height, chlorophyll content, relative water content, and grain yield. Conversely, traits like leaf rolling and sterility percentage increase, indicating the negative impact of water deficit environment on rice growth (Volante et al., 2017; Hoang et al., 2019). The genetic response to water deficit in rice involves the regulation of numerous genes and TFs that control stress-responsive pathways. For instance, genes related to ABA biosynthesis, osmotic adjustment, and ROS detoxification are upregulated to enhance drought tolerance. Moreover, genome-wide association studies (GWAS) have identified specific quantitative trait loci (QTLs) associated with drought tolerance traits, which can be targeted in breeding programs to develop rice varieties with improved drought tolerance (Volante et al., 2017; Hoang et al., 2019). Through hybridization and backcrossing, some drought-tolerant traits have been transferred to modern rice varieties, improving their performance under drought conditions. By using CRISPR/Cas9 gene-editing technology, genes that inhibit rice drought tolerance have been knocked out, thereby enhancing their growth and yield under drought conditions. The combination of physiological, biochemical, and genetic approaches is crucial for improving rice drought tolerance and ensuring stable yields under water deficit conditions.
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