Molecular Plant Breeding 2025, Vol.16, No.3, 165-179 http://genbreedpublisher.com/index.php/mpb 167 2.3 Molecular responses and signaling pathways At the molecular level, rice plants activate a complex network of signaling pathways and gene expression changes in response to drought stress. Key signaling molecules such as ABA play a central role in drought response by regulating stomatal closure and inducing the expression of drought-responsive genes (Shinozaki and Yamaguchi-Shinozaki, 2006). Former research has identified two primary regulatory pathways that influence gene expression patterns related to drought resistance mechanisms: (1) ABA-dependent pathways and (2) ABA-independent pathways. The ABA-dependent pathway is driven by MYB, NAC, and AREB/ABF TFs, whereas the ABA-independent pathways are regulated by DREB TFs (Du et al., 2011; Fu et al., 2017). TFs like DREB (dehydration-responsive element-binding), AREB/ABF (ABA-responsive element-binding protein/ABRE-binding factor), and NAC (NAM, ATAF, and CUC) are crucial for the activation of downstream drought-responsive genes that encode for osmoprotectants, late embryogenesis abundant (LEA) proteins, and heat shock proteins (HSPs) (Nakashima et al., 2007). Additionally, rice plants utilize microRNAs (miRNAs) to fine-tune gene expression during drought stress. For example, miR169 and miR393 have been shown to regulate genes involved in stress responses and hormone signaling pathways (Zhao et al., 2007). In response to drought, rice plants generate ROS, which act as signaling molecules in stress adaptation. Low to moderate ROS levels trigger the activation of stress-responsive TFs and antioxidant defenses. ROS interact with other signaling pathways, such as ABA and MAPK, to mediate drought responses (Mittler et al., 2011). The integration of these physiological and molecular responses enables rice plants to survive and adapt to drought conditions. Understanding these mechanisms provides valuable insights for developing drought-resistant rice varieties through genetic engineering and molecular breeding approaches. 3 Identification of Drought Resistance Genes in Rice 3.1 Methods for identifying drought resistance genes Identifying drought resistance genes in rice involves a combination of traditional and modern molecular techniques. GWAS have been instrumental in identifying loci associated with drought resistance traits. A study utilized a non-destructive phenotyping facility to extract 51 image-based traits (i-traits) from 507 rice accessions, leading to the identification of 470 association loci, some containing known drought resistance (DR)-related genes (Guo et al., 2018). Additionally, genetic linkage maps and QTL mapping have been used to dissect the genetic basis of drought resistance. A comprehensive study mapped QTLs for osmotic adjustment and root traits in a doubled-haploid rice population, identifying 41 QTLs that explained 8%~38% of the phenotypic variance (Zhang et al., 2022). Transcriptomic analyses and gene co-expression networks also play a crucial role in identifying differentially expressed genes (DEGs) under drought conditions, as demonstrated by the identification of key modules and hub genes associated with drought sensitivity in rice (Yu et al., 2020). 3.2 Key drought resistance genes discovered in rice Several key drought resistance genes have been discovered in rice through various studies. The OsPP15 gene, identified through GWAS and confirmed by genetic transformation experiments, plays a significant role in drought resistance (Guo et al., 2018). Another study highlighted the role of the AP2/ERF TF family member OsERF71, which, when overexpressed, conferred a drought-resistant phenotype by modulating global gene expression to prioritize survival-critical mechanisms (Ahn et al., 2017). Additionally, a meta-analysis of QTLs identified stable QTLs across different genetic backgrounds and environments, pinpointing genes such as ABA-Insensitive Protein 5 (ABI5) and G-box binding factor 4 (GBF4) as crucial for drought response (Selamat and Nadarajah, 2021). DREB1 and DREB2 have been extensively studied for their role in drought tolerance. These genes bind to dehydration-responsive elements (DRE) in the promoter regions of stress-inducible genes and activate their expression, leading to improved drought tolerance (Lata and Prasad, 2011). Furthermore, genes like WRKYs and PR family proteins have been identified as differentially expressed hub genes involved in ROS scavenging, contributing to drought resistance (Yu et al., 2020). Successful drought-resistant advantages of upland rice have motivated researchers to explore related genetic mechanisms. Sun et al. (2022) found that the elite haplotype of DROUGHT1 (DROT1) exists in upland rice, and the key SNP variation in the promoter region results in higher expression of DROT1, thereby enhancing drought
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