TaSPX3 Enhances Wheat Resistance to Leaf Rust by Antagonising TaDi19-Mediated Repression of Pathogenesis-Related...

Wheat leaf rust, caused by Puccinia triticina (Pt), threatens global wheat production, with yield losses further exacerbated by the pathogen's evolving virulence. Although Syg1/Pho81/Xpr1 (SPX) domain-containing proteins are known regulators of phosphate homeostasis, their involvement in plant-pathogen interactions remains largely unexplored. We demonstrated that TaSPX3, a wheat SPX family gene, is rapidly induced during early Pt infection and flg22 treatment. Genetic evidence indicates that TaSPX3 is a positive regulator of rust resistance, with knockdown lines showing increased susceptibility and overexpression lines exhibiting enhanced resistance. Using yeast two-hybrid screening, we identified TaDi19-1D, a zinc finger transcription factor, as a direct TaSPX3 interactor. TaDi19-1D functions as a negative immune regulator by suppressing the expression of pathogenesis-related (PR) genes (TaPR1, TaPR2, TaPR5) through direct promoter binding. TaSPX3 counteracts this repression by physically interacting with TaDi19-1D, thereby derepressing PR gene expression and boosting wheat resistance to Pt. Our findings revealed a novel TaSPX3-TaDi19 regulatory module that fine-tunes TaPRs expression, providing mechanistic insights into pattern-triggered immunity (PTI) and potential genetic targets for breeding durable broad-spectrum disease-resistant wheat varieties.