Phosphite, an analog of phosphate, counteracts Phosphate Induced Susceptibility of rice to the blast fungus Magnaporthe oryzae

Phosphate (Pi) and phosphite (Phi), a non-metabolizable analogue of Pi, are taken up by plant roots through the same transport system. Whereas Pi is an essential nutrient for plants, Phi might function as a biostimulant and in protection against pathogens. However, how Phi mechanistically exerts beneficial effects on plants remains unsolved. We examined the impact of Phi and Pi on Arabidopsis thaliana and rice growth and upon pathogen infection. Phi inhibited the in vitro growth of Plectosphaerella cucumerina and Fusarium fujikuroi in a dose-dependent manner, whereas Magnaporthe oryzae growth was largely unaffected. Phis effect on plant growth was dependent on the plant species, the basal Pi level in the plant, and the ratio Pi to Phi. In Arabidopsis, Phi enhanced resistance to P. cucumerina by triggering a hypersensitive response-like cell death. Notably, Phi reversed Pi-induced susceptibility to blast (M. oryzae) and bakanae (F. fujikuroi) diseases in rice. Transcriptomic analysis revealed that Phi triggered extensive reprogramming in rice under high Pi, including the activation of signaling pathways enriched in phosphorylation-dependent processes, while attenuating induction of carbon metabolism. Phi acts as a multifaceted agent, promotes balanced metabolic state, improved plant performance, and reduced Pi-induced disease susceptibility when applied under appropriate Pi conditions. HighlightPhosphite application confers protection against fungal pathogens in Arabidopsis and rice plants by regulating signaling pathways depending on phosphorylation processes.