Molecular mechanisms of strigolactone biosynthesis and signaling in low phosphorus response in rice. Oryza sativa

Phosphorus is an essential macronutrient for plant development and metabolism. Plants have evolved ingenious mechanisms to overcome phosphate (Pi) starvation. However, elucidating molecular mechanisms underlying the regulation of shoot and root architecture and the coordinated utilization of Pi and nitrogen remains challenging. Here, we showed that NODULATION SIGNALING PATHWAY 1 (NSP1) and NSP2 regulate tiller number by activating the biosynthesis of strigolactones (SLs), which are a class of phytohormones with fundamental effects on plant architecture and environmental responses. In response to low-Pi stress, NSP1 and NSP2 are induced and form a complex to directly bind the promoters of SL biosynthesis genes, playing essential roles in the induction of SL biosynthesis in rice. Oryza sativa PHOSPHATE STARVATION RESPONSE2 (OsPHR2) also directly binds and activates promoters of SL biosynthesis genes to improve SL production. The NSP1/2-SL signaling module represses the expression of CROWN ROOTLESS 1 (CRL1), a newly identified early SL responsive gene in roots, to restrain lateral root density under Pi deficiency. Furthermore, GR244DO treatment under normal conditions can repress expression of OsNRTs and OsAMTs to suppress nitrogen absorption, while enhance OsPTs expression to promote Pi absorption, thus facilitating the balance of nitrogen and phosphorus in rice. Importantly, the NSP1p:NSP1 and NSP2p:NSP2 transgenic plants showed improved agronomic traits and grain yield under low and medium phosphorus conditions. Taken together, our results uncovered the mechanisms of SL biosynthesis and signaling in response to Pi starvation stress and provided genetic resources to improve plant architecture and nutrient use efficiency under low Pi environments.