Molecular Soil Biology 2025, Vol.16, No.6, 287-296 http://bioscipublisher.com/index.php/msb 292 soil is in a flooded state, these structural changes can enhance the ability of the roots to transport oxygen downward. In drought conditions, they help the roots retain water and regulate the lateral movement of water in the roots. 6 Molecular Responses of Root Development Genes to Soil Stress 6.1 Transcriptional and epigenetic responses of root genes to drought stress Phenotypic screening of 106 rice accessions under PEG-simulated drought conditions at 1, 3, and 7 days showed that the drought-tolerant variety Heena significantly outperformed the sensitive variety Kiran in root length, root hair number, secondary and adventitious root number, lignin deposition, and vessel area, and maintained higher relative water content and biomass under drought (Tiwari et al., 2020). The two varieties had 1033 and 936 specifically upregulated differentially expressed genes in their roots, respectively. Upregulated genes in Heena were enriched in hormone signaling (especially ABA, JA, and ethylene), typical stress-related genes (LEA, DREB), and numerous transcription factors (AP2/ERF, MYB, WRKY, bHLH), accompanied by enhanced photosynthesis and antioxidant pathways, while Kiran mainly showed oxidative stress and damage response pathways. In Azucena, Z1 (meristematic/elongation phase) showed significant enrichment of cell cycle, cell division, root growth, and development-related genes under drought, while IR64 Z1 was enriched in oxidative stress response genes. Among the 375 strongly upregulated genes in Azucena Z1, 40 were clearly annotated as key genes for root structure and drought tolerance, including OsbHLH120 and OsNAC10 regulating root diameter, OsPHR3 for lateral root development, aquaporin PIP1;3/RWC3 for water avoidance, and OsMADS18, OsNLA1, etc., related to root length (Abdirad et al., 2022) (Figure 1). Figure 1 Root sampling and phenotypic responses of two contrasting rice genotypes, Azucena and IR64, to water stress (Adopted from Abdirad et al., 2022)
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