Rice blast caused by the fungus Magnaporthe oryzae is the most devastating fungal disease of rice worldwide. To reduce losses due to M. oryzae infection, and to obtain maximum yields, high amounts of pesticides and fertilizers continue to be applied in rice cultivation causing an adverse impact on human health and environment. It is also known that nutrition might have an impact on disease severity and, in some cases, excess of fertilization might have negative efects on disease resistance. Although adaptation to nutrient supply conditions and immunity are not independent processes, the molecular mechanisms involved in nutrient stress responses and innate immunity have been so far investigated separately from each other. In this study, we investigated the efect of phosphate (Pi) supply on resistance to infection by the blast fungus M. oryzae in rice, focusing on the two partners of the interaction. On the plant side, we found that high Pi fertilization, and subsequent Pi accumulation, enhances blast susceptibility which is associated to a weaker activation of defense related genes during M. oryzae infection. Regarding the pathogen, confocal microscopy of rice sheaths inoculated with a M. oryzae strain co-expressing two genes encoding fuorescently-labeled efectors (PWL2 and BAS4) revealed early induction of M. oryzae efectors in rice plants that have been grown under high Pi supply. Overall, these results support that Pi accumulation has an efect on the two partners of the interaction, host and pathogen, by undermining host defense programmes and stimulating fungal pathogenicity. Cross-talk between the two signalling pathways, Pi signalling and immune signalling, would then play an essential role in controlling blast susceptibility in rice. These fndings illustrate the fact that the indiscriminate use of Pi fertilizers might have adverse efects on the rice plant by increasing the likelihood of blast disease. A better understanding of the interconnected regulations between nutrient (Pi) supply and disease resistance will lay a foundation for rationally optimizing fertilizer and pesticide use in rice production.

Trabajo presentado en el XVI Meeting of Plant Molecular Biology, celebrado en Sevilla entre el 14 y el 16 de septiembre de 2022.