OsAAI1-OsMADS25 module orchestrates root morphogenesis by fine-tuning IAA in drought stressed rice

Indole-3-acetic acid (IAA) plays a critical role as a plant hormone in regulating the growth and development of the root system in plants, particularly in enhancing their ability to withstand abiotic stress. In this study, we found that overexpression of OsAAI1 promoted the growth of rice root system. The length of primary root, the number of lateral roots, the density of lateral roots, and the number of adventitious roots of overexpression of OsAAI1 (OE19) were significantly better than those of the wild type (ZH11) and the mutant line (osaai1), and the IAA content of OE19 was significantly higher than those of ZH11 and osaai1. We also found that exogenous application of IAA could compensate for the root growth defect caused by the osaai1 mutation. OE19 had the highest number and widest distribution of total roots under the water-cut drought treatment, and exogenous application of IAA attenuated the growth inhibitory effect of drought stress on osaai1. Our study also revealed that OsAAI1 interacts with the MADS-box family transcription factor OsMASD25. Additionally, the application of IAA helped alleviate the growth inhibitory effects of drought stress on osmads25.Importantly, OsMADS25 interaction with OsAAI1 was found to enhance the transcriptional expression of its downstream target genes LAX1 and OsBAG4, which are crucial genes in rices response to drought stress. These findings suggest that OsAAI1 and OsMADS25 are crucial in rices drought acclimation process by regulating downstream gene expression and influencing the IAA signaling pathway. Author summaryThe root system is a crucial organ for crop plants as it facilitates the absorption of water and nutrients, contributing to their drought resistance. Indole-3-acetic acid (IAA) plays a pivotal role in the growth of various types of roots in plants. Under drought stress conditions, changes in IAA levels and transport can impact the morphology of plant roots. This research illustrates that OsAAI1 positively influences rice root development and enhances the plants response to drought stress through the auxin signaling pathway. The study reveals a physical interaction between OsAAI1 and the transcription factor OsMADS25. This interaction boosts the expression of the auxin synthesis gene OsYUC4 and suppresses the auxin inhibitory factor OsIAA14, thereby promoting the auxin signaling pathway, stimulating rice root growth, and enhancing the plants ability to withstand drought. Furthermore, the interaction between OsAAI1 and OsMADS25 has been found to also positively affect the expression of the genes LAX1 and OsBAG4, which is associated with activated drought resistance in rice plants.