Rice false smut fungus hijacks rice lipid signalling to manipulate floret development and immunity

Rice false smut, caused by Ustilaginoidea virens, increases the proportion of unfilled grains and reduces pollen viability in infected rice panicles. Although the fungus adopts a flower-specific infection strategy that interferes with fertilization, the underlying molecular mechanisms remain unclear. Here we show that U. virens manipulates rice floret development and immune responses during early infection by targeting host lipid signalling. We identified secreted in xylem protein 1 (Sxp1) as a secreted apoplastic effector induced under nutrient-rich conditions and during early infection. Ectopic expression of Sxp1 in rice causes near-complete spikelet sterility and markedly reduced pollen viability. Sxp1 is a key virulence factor and interacts with the lipid transfer protein LTPL113, which binds phosphatidic acid and phosphatidylserine, and is essential for pollen development and lipid-potentiated immune outputs. Sxp1 disrupts the association between LTPL113 and lipids, thereby compromising lipid-mediated immunity and floret development. Together, our findings reveal a mechanism by which U. virens hijacks lipid signalling to manipulate floret development and suppress immunity.