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 NH 4 + uptake and stress response of plants is unclear. Here, we observed that mutation in indeterminate domain 10 (IDD10), a key transcription factor in NH 4 + signaling, led to NH 4 + -sensitive root growth in light but not in dark. Genetic combinations of idd10 and phy mutants demonstrated that phyB, but not phyA or phyC, suppressed NH 4 + -sensitive root growth of idd10. PhyB mutants and overexpressors (PhyB OXs) accumulated more and less NH 4 + , respectively, compared with wild-type. RT-qPCR revealed that PhyB negatively regulated NH 4 + -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 NH 4 + condition. This suggested that NH 4 + uptake might be positively associated with the root growth. Further, PhyB interacted with and inhibited IDD10 and brassinazole resistant 1 (BZR1). IDD10 interacted with BZR1 to activate AMT1;2. NH 4 + uptake is known to promote resistance of rice 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 saline-alkaline response, whereas PhyB-BZR1-AMT1;2 pathway modulates ShB resistance. Collectively, the data proved that mutation in PhyB gene promoted the resistance of rice to ShB and saline-alkaline stress by increasing NH 4 + uptake.