Physiological and Molecular Characterization of the Drought Tolerance-Related QTL qDTY12.1 in Japonica Rice

Drought tolerance in rice is a complex trait regulated by multiple genetic and physiological factors. The quantitative trait locus qDTY12.1 has been associated with improved rice drought resilience, but, the drought tolerance conferred by qDTY12.1 in japonica rice remains unexplored. This study investigated the physiological, morphological, and molecular impacts of qDTY12.1 introgression in two rice cultivars, TN11 and TK14. Detached leaf water loss assays revealed that qDTY12.1 introgression lines maintained higher leaf water content than their recurrent parents. Under drought conditions, these lines exhibited moderated reductions in stomatal conductance and stable carbon isotopes discrimination, indicating improved water-use efficiency. Although biomass and yield-related traits were not significantly altered, the TK14_12.1 line consumed less water during vegetative growth. Root phenotyping showed enhanced drought-induced development of thicker and deeper root angles in introgression lines. Biochemically, qDTY12.1 lines accumulated less proline under stress, with distinct expression patterns of proline metabolism and transport genes. Transcriptome analysis under drought and well-watered conditions identified numerous differentially expressed genes (DEGs), including several aquaporins and genes located within the qDTY12.1 chromosomal interval. Notably, the expression of genes potentially involved in stress responses, hormone signaling, and redox regulation was altered in a genotype-dependent manner. These findings suggest that qDTY12.1 modulates complex physiological and transcriptional networks to improve drought adaptation, with variable effects depending on genetic background.