Mutation of phytochrome B promotes resistance to sheath blight and saline-alkaline stress via increasing ammonium uptake in rice

Phytochrome B (PhyB), a red-light receptor, plays important roles in diverse biological processes in plants; however, its function in NH4+ uptake and stress responses of plants is unclear. Here, we observed that mutation in indeterminate domain 10 (IDD10), which encodes a key transcription factor in NH4+ signaling, led to NH4+-sensitive root growth in light but not in the dark. Genetic combinations of idd10 and phy mutants demonstrated that phyB, but not phyA or phyC, suppressed NH4+-sensitive root growth of idd10. PhyB mutants and PhyB overexpressors (PhyB OXs) accumulated more and less NH4+, respectively, compared with wild-type plants. Real time quantitative polymerase chain reaction (RT-qPCR) revealed that PhyB negatively regulated NH4+-mediated induction of Ammonium transporter 1;2 (AMT1;2). AMT1 RNAi plants with suppressed AMT1;1, AMT1;2, and AMT1;3 expression exhibited shorter primary roots under NH4+ conditions. This suggested that NH4+ uptake might be positively associated with root growth. Further, PhyB interacted with and inhibited IDD10 and brassinazole-resistant 1 (BZR1). IDD10 interacted with BZR1 to activate AMT1;2. NH4+ uptake is known to promote resistance of rice (Oryza sativa) to sheath blight (ShB) and saline-alkaline stress. Inoculation of Rhizoctonia solani demonstrated that PhyB and IDD10 negatively regulated and AMT1 and BZR1 positively regulated resistance of rice to ShB. In addition, PhyB negatively regulated and IDD10 and AMT1 positively regulated resistance of rice to saline-alkaline stress. This suggested that PhyB-IDD10-AMT1;2 signaling regulates the saline-alkaline response, whereas the PhyB-BZR1-AMT1;2 pathway modulates ShB resistance. Collectively, these data prove that mutation in the PhyB gene enhances the resistance of rice to ShB and saline-alkaline stress by increasing NH4+ uptake.