OsHyPRP06/R3L1 regulates root system development and salt tolerance via apoplastic ROS homeostasis in rice (Oryza sativa L.).

Plant root morphology is constantly reshaped in response to triggers from the soil environment. Such modifications in root system architecture involve changes in the abundance of reactive oxygen species (ROS) in the apoplast and in cell wall (CW) composition. The hybrid proline-rich proteins (HyPRPs) gene family in higher plants is considered important in the regulation of CW structure. However, the functions of HyPRPs remain to be characterized. We therefore analysed the functions of OsR3L1 (Os04g0554500) in rice. qRT-PCR and GUS staining revealed that OsR3L1 is expressed in roots. While the r3l1 mutants had a defective root system with fewer adventitious roots (ARs) and lateral roots (LRs) than the wild type, lines overexpressing OsR3L1 (R3L1-OE) showed more extensive LR formation but with a shorter root length. The expression of OsR3L1 was initiated by the OsMADS25 transcription factor. Moreover, the abundance of OsR3L1 transcripts was increased by NaCl. The R3L1-OE-3 line exhibited enhanced salt tolerance, whereas the r3l1-2 mutant showed greater salt sensitivity. The addition of H O increased the levels of OsR3L1 transcripts. Data are presented indicating that OsR3L1 modulates H O accumulation in the apoplast. We conclude that OsR3L1 regulates salt tolerance through regulation of peroxidases and apoplastic H O metabolism.