Spatially distinct regulation of strigolactone exudation by phosphate and phytohormones in rice

Strigolactones (SLs) are carotenoid-derived phytohormones that shape plant architecture and function as rhizosphere signals promoting arbuscular mycorrhizal symbiosis. In rice, SL exudation is strongly induced by phosphate (Pi) deficiency and suppressed when Pi is sufficient, yet how local and systemic cues coordinate this output remains unclear. Using a split-root system, we show that Pi acts as a systemic suppressor of SL exudation: local Pi supply repressed SL release from both treated and untreated root halves. By contrast, cytokinin, salicylic acid, jasmonic acid, and the ethylene precursor ACC suppressed SL exudation mainly in the treated compartment, indicating predominantly local control. Transcriptome profiling revealed a coordinated systemic Pi response in roots and a distinct Pi-specific shoot program, including repression of Pi starvation responses and activation of translation- and chloroplast-related functions, which was not reproduced by hormone treatments. We further identified a small set of commonly regulated root genes across SL-suppressing conditions, including OsPDR family members whose expression patterns track changes in SL exudation. Our findings define Pi as a long-distance regulator of SL exudation and highlight local hormonal pathways that converge on downstream processes controlling SL production and/or export.